Bitwise compress incomplete epoch slots

[pgarg66]

Problem

Incomplete slot information in EpochSlots could cause the message to grow larger than MTU size. The current message format is not ABI forward compatible with changes required to split it in MTU sized chunks.

Summary of Changes

1. Add an index field to EpochSlots gossip message
2. Store slots as bits in the compressed list
3. Store multiple bitmaps so that disjoint incomplete slot information can be transmitted over multiple packets.

[aeyakovenko]

Perfect!

[codecov]

Codecov Report

Merging #8341 into master will increase coverage by <.1%.
The diff coverage is 91.6%.

@@           Coverage Diff            @@
##           master   #8341     +/-   ##
========================================
+ Coverage    80.5%   80.5%   +<.1%     
========================================
  Files         253     253             
  Lines       55412   55416      +4     
========================================
+ Hits        44637   44642      +5     
+ Misses      10775   10774      -1

[mvines]

This needs to be backported to 0.23 since it's an ABI change to Gossip, and thus must be picked up when we restart TdS

[pgarg66]

This needs to be backported to 0.23 since it's an ABI change to Gossip, and thus must be picked up when we restart TdS

@mvines in that case, this should be backported as well. #8276

The current PR is dependent on 8276