feat: add an option for selecting priv key type

[egonspace]

Closes: #XXX

Description

Added an option for selecting private key type on the tendermint init command.

Usage:

$ tendermint init --help
Initialize Tendermint

Usage:
  tendermint init [flags]

Flags:
  -h, --help                   help for init
      --priv_key_type string   Specify validator's private key type (ed25519 | composite) (default "ed25519")

Global Flags:
      --home string        directory for config and data (default "/Users/user/.tendermint")
      --log_level string   Log level (default "main:info,state:info,*:error")
      --trace              print out full stack trace on errors

$ tendermint init   ## create an ed25519 key by default

$ tendermint init --priv_key_type=ed25519
$ tendermint init --priv_key_type=composite

$ tendermint init --priv_key_type=ed25518
ERROR: undefined private key type: ed25518

---

For contributor use:

• Wrote tests
• Updated CHANGELOG_PENDING.md
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Updated relevant documentation (docs/) and code comments
• Re-reviewed Files changed in the Github PR explorer

[github-actions]

[golangci] _{reported by reviewdog 🐶}
ifElseChain: rewrite if-else to switch statement (gocritic)

[github-actions]

[golangci] _{reported by reviewdog 🐶}
File is not gofmt-ed with -s (gofmt)

[egonspace]

About modifying of circleci config:
There was the error when we were building contract-tests with ubuntu20.10 in circleci

Hooks handler stderr: /home/circleci/.go_workspace/src/github.com/tendermint/tendermint/build/contract_tests: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by /home/circleci/.go_workspace/src/github.com/tendermint/tendermint/build/contract_tests)

I don't know exactly why this error occurs, but it seems to be a problem that occurs probably because the shared library referenced by libc.so.6 in ubuntu20.10, an environment that builds contract-tests, is not present in the linux environment running contract-tests. To correct this, ubuntu19.10 was used.

[egonspace]

I will switch the base branch from feat/add_metric to develop after feat/add_metric would be merged.

[kukugi]

LGTM 👍

[torao]

LGTM

[torao]

I feel the name composite seems a bit vague. What about ed25519+bls, ed25510/bls, etc., to clarify that it's an Ed25519 and BLS composite key.

[egonspace]

We are already using the name 'composite' in genesis.json and priv_validator_key.json files.
I think it is better to use the same term for unity.

  "consensus_params": {
    "block": {
      "max_bytes": "22020096",
      "max_gas": "-1",
      "time_iota_ms": "1000"
    },
    "evidence": {
      "max_age_num_blocks": "100000",
      "max_age_duration": "172800000000000"
    },
    "validator": {
      "pub_key_types": [
        "ed25519",
        "composite"
      ]
    }

{
  "address": "71463258B3E4A84F7EF1CB54473927726DAF6076",
  "pub_key": {
    "type": "tendermint/PubKeyComposite",
    "value": {
      "sign": {
        "type": "tendermint/PubKeyBLS12",
        "value": "hgq9S306jqNyqQeSX6YXBHV+BmNhoHG80BmuMdbRGyGWjyuDqJl83n+O8c79V9UY"
      },
      "vrf": {
        "type": "tendermint/PubKeyEd25519",
        "value": "afUwO/WEjC5l/0/DFM2OLu99n5FGz7pJtEWXqM8loOI="
      }
    }
  },
  "priv_key": {
    "type": "tendermint/PrivKeyComposite",
    "value": {
      "sign": {
        "type": "tendermint/PrivKeyBLS12",
        "value": "DiGI+49LV82oAMod+tu2P9SbqkU08soDbNc1UhsXDW8="
      },
      "vrf": {
        "type": "tendermint/PrivKeyEd25519",
        "value": "zcwkHxXUoSTxIa1lNmxA74jzEwMX+SfiIFwMkzqeycpp9TA79YSMLmX/T8MUzY4u732fkUbPukm0RZeozyWg4g=="
      }
    }
  }
}