feat: implement ADR-019: Subspace post migration

Description

This PR implements ADR-019: Subspace post migration.

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 in the PR title
[ ] added ! to the type prefix if API or client breaking change
[x] targeted the correct branch (see PR Targeting)
[ ] provided a link to the relevant issue or specification
[ ] followed the guidelines for building modules
[x] included the necessary unit and integration tests
[ ] added a changelog entry to CHANGELOG.md
[ ] included comments for documenting Go code
[ ] updated the relevant documentation or specification
[x] reviewed "Files changed" and left comments if necessary
[ ] confirmed all CI checks have passed

Reviewers Checklist

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I have...

[ ] confirmed the correct type prefix 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)

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.17 :tada:

Comparison is base (fdb18ed) 80.12% compared to head (6482721) 80.30%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1157 +/- ## ========================================== + Coverage 80.12% 80.30% +0.17% ========================================== Files 189 189 Lines 16526 16675 +149 ========================================== + Hits 13242 13391 +149 Misses 2690 2690 Partials 594 594 ``` | [Impacted Files](https://app.codecov.io/gh/desmos-labs/desmos/pull/1157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=desmos-labs) | Coverage Δ | | |---|---|---| | [x/posts/keeper/msg\_server.go](https://app.codecov.io/gh/desmos-labs/desmos/pull/1157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=desmos-labs#diff-eC9wb3N0cy9rZWVwZXIvbXNnX3NlcnZlci5nbw==) | `91.99% <100.00%> (+1.57%)` | :arrow_up: | | [x/posts/keeper/polls.go](https://app.codecov.io/gh/desmos-labs/desmos/pull/1157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=desmos-labs#diff-eC9wb3N0cy9rZWVwZXIvcG9sbHMuZ28=) | `97.89% <100.00%> (+0.19%)` | :arrow_up: | | [x/posts/types/models.go](https://app.codecov.io/gh/desmos-labs/desmos/pull/1157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=desmos-labs#diff-eC9wb3N0cy90eXBlcy9tb2RlbHMuZ28=) | `79.03% <100.00%> (+1.66%)` | :arrow_up: | | [x/posts/types/msgs.go](https://app.codecov.io/gh/desmos-labs/desmos/pull/1157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=desmos-labs#diff-eC9wb3N0cy90eXBlcy9tc2dzLmdv) | `97.53% <100.00%> (+0.32%)` | :arrow_up: | ... and [3 files with indirect coverage changes](https://app.codecov.io/gh/desmos-labs/desmos/pull/1157/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=desmos-labs)

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desmos-labs / desmos