Update authz expire to make it optional

[robert-zaremba]

Summary

Today, autz expire is not optional, against it's design.

Proposal

1. Remove nullable = false in

   cosmos-sdk/proto/cosmos/authz/v1beta1/authz.proto

   Lines 22 to 27 in a7fb1a1

   	// Grant gives permissions to execute
   	// the provide method with expiration time.
   	message Grant {
   	google.protobuf.Any authorization = 1 [(cosmos_proto.accepts_interface) = "Authorization"];
   	google.protobuf.Timestamp expiration = 2 [(gogoproto.stdtime) = true, (gogoproto.nullable) = false];
   	}

2. Don't add to the expiration queue if there's no expiration date (depends on feat(authz)!: pruning expired authorizations #10714)

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[likhita-809]

@robert-zaremba did you start working on this ?
If not, I can do so.

[amaury1093]

This issue actually depends on #10714.

I'm wondering if we can do it all at once in one PR. What do you think @aleem1314 ?

[aleem1314]

I'm wondering if we can do it all at once in one PR. What do you think @aleem1314 ?

I think @robert-zaremba working on this. There is a draft PR 11060.

[robert-zaremba]

Yes, let's firstly merge #10714

[robert-zaremba]

This one also depends on: cosmos/cosmos-proto#60 , so please review