implements ping-pong packets between nodes (bp #12794)

[mergify]

This is an automated backport of pull request #12794 done by Mergify

Cherry-pick of ae91270 has failed:

On branch mergify/bp/v1.3/pr-12794
Your branch is up to date with 'origin/v1.3'.

You are currently cherry-picking commit ae9127096.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:

	modified:   core/Cargo.toml
	modified:   core/src/crds_gossip.rs
	modified:   core/src/crds_gossip_pull.rs
	modified:   core/src/lib.rs
	new file:   core/src/ping_pong.rs
	modified:   core/tests/crds_gossip.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)

	both modified:   Cargo.lock
	both modified:   core/src/cluster_info.rs

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[mergify]

automerge label removed due to a CI failure

[codecov]

Codecov Report

Merging #13281 into v1.3 will decrease coverage by 0.0%.
The diff coverage is 72.6%.

@@           Coverage Diff            @@
##            v1.3   #13281     +/-   ##
========================================
- Coverage   82.2%    82.1%   -0.1%     
========================================
  Files        351      366     +15     
  Lines      81640    85338   +3698     
========================================
+ Hits       67153    70116   +2963     
- Misses     14487    15222    +735