chore: Add proto comments for MsgCreatePeriodicVestingAccountResponse (…

…#10007)

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## Description

We merged #9596, but we forgot to add proto comments for one message.

Then, proto lint CI fails on unrelated PRs, e.g. https://github.com/cosmos/cosmos-sdk/pull/9759/checks?check_run_id=3421076482#step:4:24. This fixes it.

Also related to #9978

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---

### 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
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [x] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] 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/core/proto-docs.md

@@ -9568,7 +9568,8 @@ account.
 <a name="cosmos.vesting.v1beta1.MsgCreatePeriodicVestingAccountResponse"></a>
 
 ### MsgCreatePeriodicVestingAccountResponse
-
+MsgCreateVestingAccountResponse defines the Msg/CreatePeriodicVestingAccount
+response type.
 
 
 

proto/cosmos/vesting/v1beta1/tx.proto

@@ -46,4 +46,6 @@ message MsgCreatePeriodicVestingAccount {
   repeated Period vesting_periods = 4 [(gogoproto.nullable) = false];
 }
 
+// MsgCreateVestingAccountResponse defines the Msg/CreatePeriodicVestingAccount
+// response type.
 message MsgCreatePeriodicVestingAccountResponse {}