docs: folding module specs files into single README file (#1369)

## Description

Following the Cosmos SDK updates, let's fold spec files into a README file, and put more specific things into the spec directory.

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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...

- [ ] 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
- [ ] added appropriate labels to the PR
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/umee-network/umee/blob/main/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] 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 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)