docs: improve proto vesting docs about time attributes (backport #15474)

[mergify]

This is an automatic backport of pull request #15474 done by Mergify.
Cherry-pick of 5612bb8 has failed:

On branch mergify/bp/release/v0.47.x/pr-15474
Your branch is up to date with 'origin/release/v0.47.x'.

You are currently cherry-picking commit 5612bb815.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   api/cosmos/vesting/v1beta1/vesting.pulsar.go
	modified:   x/auth/vesting/types/vesting.pb.go

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   api/cosmos/vesting/v1beta1/tx.pulsar.go
	deleted by us:   client/v2/internal/testpb/msg.proto
	both modified:   orm/internal/testpb/bank.proto
	both modified:   proto/cosmos/vesting/v1beta1/tx.proto
	both modified:   proto/cosmos/vesting/v1beta1/vesting.proto
	deleted by us:   tests/integration/aminojson/internal/testpb/test.proto
	both modified:   x/auth/vesting/types/tx.pb.go
	deleted by us:   x/tx/internal/testpb/signers.proto

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[julienrbrt]

Note to self, we should avoid linting in a PR that will be backported.

[tac0turtle]

Note to self, we should avoid linting in a PR that will be backported.

everything that is cosmetic shouldnt be backported 😉

[julienrbrt]

Ran make proto-gen and it did the same thing as here: #15268.
I think we should commit it to avoid noise in future PRs as we did for #15268.

[robert-zaremba]

Note to self, we should avoid linting in a PR that will be backported.

Agree, sorry, it came automatically for some reason.

[robert-zaremba]

Thanks for backporting the PR @julienrbrt !