new checks for deprecated manifest hashes

[arthurzam]

2 new checks:

• RepoManifestHashCheck: check for deprecated repo config
• DeprecatedManifestHash: check for deprecated checksums in manifest files

Resolves: https://github.com/pkgcore/pkgcheck/issues/508

[codecov[bot]]

Codecov Report

Patch coverage: 78.04% and project coverage change: +0.01 :tada:

Comparison is base (123abbc) 79.75% compared to head (2b9b8e7) 79.77%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #598 +/- ## ========================================== + Coverage 79.75% 79.77% +0.01% ========================================== Files 58 58 Lines 8621 8652 +31 Branches 1961 1966 +5 ========================================== + Hits 6876 6902 +26 - Misses 1643 1648 +5 Partials 102 102 ``` | [Impacted Files](https://app.codecov.io/gh/pkgcore/pkgcheck/pull/598?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pkgcore) | Coverage Δ | | |---|---|---| | [src/pkgcheck/checks/repo\_metadata.py](https://app.codecov.io/gh/pkgcore/pkgcheck/pull/598?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pkgcore#diff-c3JjL3BrZ2NoZWNrL2NoZWNrcy9yZXBvX21ldGFkYXRhLnB5) | `67.60% <78.04%> (+1.08%)` | :arrow_up: |

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