feat: value renderer for timestamp protos (#12860)

## Description

Closes: #12709



Part of Sign Mode Textual (ADR 050) implementation.

Renders Timestamp messages as RFC 3339 (simplified ISO 8601).

---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [x] added `!` to the type prefix if API or client breaking change
- [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/main/CONTRIBUTING.md#pr-targeting))
- [x] provided a link to the relevant issue or specification
- [x] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/main/docs/building-modules)
- [x] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/main/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [x] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [x] updated the relevant documentation or specification
- [x] reviewed "Files changed" and left comments if necessary
- [x] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

docs/architecture/adr-050-sign-mode-textual-annex1.md

@@ -203,7 +203,20 @@ Object: /cosmos.gov.v1.Vote
 
 ### `google.protobuf.Timestamp`
 
-Rendered as either ISO8601 (`2021-01-01T12:00:00Z`).
+Rendered using [RFC 3339](https://www.rfc-editor.org/rfc/rfc3339) (a
+simplification of ISO 8601), which is the current recommendation for portable
+time values. The rendering always uses "Z" (UTC) as the timezone. It uses only
+the necessary fractional digits of a second, omitting the fractional part
+entirely if the timestamp has no fractional seconds. (The resulting timestamps
+are not automatically sortable by standard lexicographic order, but we favor
+the legibility of the shorter string.)
+
+#### Examples
+
+The timestamp with 1136214245 seconds and 700000000 nanoseconds is rendered
+as `2006-01-02T15:04:05.7Z`.
+The timestamp with 1136214245 seconds and zero nanoseconds is rendered
+as `2006-01-02T15:04:05Z`.
 
 ### `google.protobuf.Duration` (TODO)
 

tx/textual/internal/testdata/timestamp.json

@@ -0,0 +1,82 @@
+[
+    {
+        "proto": {"seconds": 1136214245},
+        "text":  "2006-01-02T15:04:05Z"
+    },
+    {
+        "proto": {"seconds": 1136214245, "nanos": 123456789},
+        "text": "2006-01-02T15:04:05.123456789Z"
+    },
+    {
+        "proto": {"seconds": 1136214245, "nanos": 123000000},
+        "text": "2006-01-02T15:04:05.123Z"
+    },
+    { "text": "", "error": true },
+    { "text": " ", "error": true },
+    { "text": "garbage", "error": true },
+    { "text": "11/30/2007", "error": true },
+    {
+        "proto": {"seconds": 0, "nanos": 0},
+        "text": "1970-01-01T00:00:00Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 1},
+        "text": "1970-01-01T00:00:00.000000001Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 10},
+        "text": "1970-01-01T00:00:00.00000001Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 100},
+        "text": "1970-01-01T00:00:00.0000001Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 1000},
+        "text": "1970-01-01T00:00:00.000001Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 10000},
+        "text": "1970-01-01T00:00:00.00001Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 100000},
+        "text": "1970-01-01T00:00:00.0001Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 1000000},
+        "text": "1970-01-01T00:00:00.001Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 10000000},
+        "text": "1970-01-01T00:00:00.01Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 100000000},
+        "text": "1970-01-01T00:00:00.1Z"
+    },
+    {
+        "proto": {"seconds": 0, "nanos": 999999999},
+        "text": "1970-01-01T00:00:00.999999999Z"
+    },
+    {
+        "proto": {"seconds": 1, "nanos": 0},
+        "text": "1970-01-01T00:00:01Z"
+    },
+    {
+        "proto": {"seconds": 2, "nanos": 0},
+        "text": "1970-01-01T00:00:02Z"
+    },
+    {
+        "proto": {"seconds": 2, "nanos": 6},
+        "text": "1970-01-01T00:00:02.000000006Z"
+    },
+    {
+        "proto": {"seconds": 1657797740, "nanos": 983000000},
+        "text": "2022-07-14T11:22:20.983Z"
+    },
+    {
+        "proto": {"seconds": -1, "nanos": 0},
+        "text": "1969-12-31T23:59:59Z"
+    }
+]

tx/textual/internal/testpb/1.proto

@@ -3,6 +3,7 @@ syntax = "proto3";
 option go_package = "cosmossdk.io/tx/textual/internal/testpb";
 
 import "google/protobuf/descriptor.proto";
+import "google/protobuf/timestamp.proto";
 import "cosmos_proto/cosmos.proto";
 import "cosmos/base/v1beta1/coin.proto";
 
@@ -22,6 +23,7 @@ message A {
   cosmos.base.v1beta1.Coin COIN           = 7;
   repeated cosmos.base.v1beta1.Coin COINS = 8;
   bytes                             BYTES = 9;
+  google.protobuf.Timestamp    TIMESTAMP = 10;
 }
 
 // B contains fields that are not parseable by SIGN_MODE_TEXTUAL, some fields