feat(p2p): persistent storage for known peers

[jansegre]

Motivation

Fixes #1036

Acceptance Criteria

• Add a peer discovery strategy that stores peer entrypoints from peers we've previously connected to on previous starts
• Use a rocksdb column family to store the entrypoints
• Enable this strategy when using a data dir, and do not enable when not using one
• Make peer manager aware of this object so it can call the appropriate methods to mark when a connection was attempted, when it successfully connected, and periodically clean up
• Add tests that covers the new module

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 14 lines in your changes missing coverage. Please review.

Project coverage is 84.96%. Comparing base (4a46f3a) to head (75ec8ff).

Files	Patch %	Lines
hathor/p2p/manager.py	31.25%	7 Missing and 4 partials ⚠️
hathor/p2p/peer_discovery/storage.py	96.70%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1056      +/-   ##
==========================================
+ Coverage   84.88%   84.96%   +0.08%     
==========================================
  Files         300      301       +1     
  Lines       22944    23054     +110     
  Branches     3471     3488      +17     
==========================================
+ Hits        19476    19588     +112     
+ Misses       2777     2776       -1     
+ Partials      691      690       -1     

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