build(deps): bump to cosmossdk.io/api v0.7.3

[julienrbrt]

Description

Closes: #19374

Attempt to use the latest api from main in release/v0.50.x to fix the issue where api v0.7.2 didn't contain the released changes from gov.

We should still verift how autocli reacts given that we will be adding unreleased things into api (normally this #18324 should nicely hide those commands, but let's see).

Once I confirm everything works in CI and locally, we can tag api v0.7.3 and bump it here.

---

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...

• included the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• reviewed "Files changed" and left comments if necessary
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• updated the relevant documentation or specification, including comments for documenting Go code
• 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 in the PR title
• confirmed all author checklist items have been addressed
• reviewed state machine logic, API design and naming, documentation is accurate, tests and test coverage

[julienrbrt]

I guess we need to fix this first:

cosmos-sdk/client/v2/internal/util/util.go

Line 26 in cd1da8d

// TODO this does not work, to fix.

otherwise autocli cannot read the since comments.

[julienrbrt]

EDIT: because we want this to be fixed sooner than later (in v0.50.4), and cosmos/cosmos-proto#131 takes longer than expected. I'll make a cosmossdk.io/api v0.7.3 cherry-picking this change, so we don't need to bump api to latest.
However, the changes from #19377 and cosmos/cosmos-proto#131 are eventually still needed.

[julienrbrt]

c0ecaf7