docs: correct spec docs of fswap module (backport #1419)

[mergify]

Description

closes: #XXXX

Motivation and context

How has this been tested?

Screenshots (if appropriate):

Checklist:

• I followed the contributing guidelines and code of conduct.
• I have added a relevant changelog to CHANGELOG.md
• I have added tests to cover my changes.
• I have updated the documentation accordingly.
• I have updated API documentation client/docs/swagger-ui/swagger.yaml

---

This is an automatic backport of pull request #1419 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 7bd6c82 has failed:

On branch mergify/bp/release/v0.49.x/pr-1419
Your branch is up to date with 'origin/release/v0.49.x'.

You are currently cherry-picking commit 7bd6c8244.
  (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:   x/fswap/keeper/keys.go
	new file:   x/fswap/spec/01_concepts.md
	new file:   x/fswap/spec/02_state.md
	new file:   x/fswap/spec/03_events.md
	deleted:    x/fswap/spec/README.md

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.75%. Comparing base (cc37bdb) to head (a8e6a70).
Report is 2 commits behind head on release/v0.49.x.

Additional details and impacted files

@@                 Coverage Diff                 @@
##           release/v0.49.x    #1429      +/-   ##
===================================================
+ Coverage            68.08%   68.75%   +0.66%     
===================================================
  Files                  770      754      -16     
  Lines                77606    75837    -1769     
===================================================
- Hits                 52840    52139     -701     
+ Misses               22097    21042    -1055     
+ Partials              2669     2656      -13     

Files	Coverage Δ
x/fswap/keeper/keys.go	81.25% <ø> (ø)

... and 84 files with indirect coverage changes