docs(epopoch-manager): add missing docummentation to structs and enum definitions

[kerber0x]

Description and Motivation

This PR adds missing docs to structs and enums on the epoch-manager.

Related Issues

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Checklist:

• [x] I have read Migaloo's contribution guidelines.
• [x] My pull request has a sound title and description (not something vague like Update index.md)
• [x] All existing and new tests are passing.
• [x] I updated/added relevant documentation.
• [x] The code is formatted properly cargo fmt --all --.
• [x] Clippy doesn't report any issues cargo clippy -- -D warnings.
• [x] I have regenerated the schemas if needed cargo schema.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 60.00000% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 91.15%. Comparing base (1d6ffbc) to head (b3d4370). Report is 34 commits behind head on release/v2_contracts.

Files	Patch %	Lines
...white-whale-std/src/epoch_manager/epoch_manager.rs	42.85%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release/v2_contracts #362 +/- ## ===================================================== Coverage 91.15% 91.15% ===================================================== Files 279 279 Lines 31119 31119 ===================================================== Hits 28368 28368 Misses 2751 2751 ```

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