p2p: get rid of interface{} from PeerStore methods

[algorandskiy]

Summary

At some point PeerStore was though to implement Phonebook interface, and as part of this some methods had interface{} in signature to accommodate both string and peer.AddrInfo. It ended up exact interface match not needed so I'm reverting this interface{} workaround.

Actually it is possible to keep addr []string in AddPersistentPeers and ReplacePeerList since they operate on single-address AddrInfo so string to AddrInfo conversion is possible.
In the same time GetAddresses returns slice of either strings (Phonebook) or generic learned peer.AddrInfo from the underlying peerstore, and no multiple addr to string conversion possible.

Test Plan

Existing tests to pass

[codecov]

Codecov Report

Attention: Patch coverage is 81.48148% with 5 lines in your changes missing coverage. Please review.

Project coverage is 56.28%. Comparing base (23a04c2) to head (ae7fc9e).
Report is 3 commits behind head on master.

Files	Patch %	Lines
network/p2p/p2p.go	0.00%	3 Missing ⚠️
network/p2pNetwork.go	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6101      +/-   ##
==========================================
+ Coverage   56.25%   56.28%   +0.03%     
==========================================
  Files         490      490              
  Lines       69699    69698       -1     
==========================================
+ Hits        39206    39230      +24     
+ Misses      27825    27802      -23     
+ Partials     2668     2666       -2     

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