Implement "openio container purge" command, remove unused code

[fvennetier]

• openio container purge can now be used to workaround Versioning is always unlimited regardless of the configuration #1163.
• M2_LEAVE RPC was no more used and has been removed.

[codecov-io]

Codecov Report

Merging #1250 into 4.x will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              4.x    #1250      +/-   ##
==========================================
+ Coverage   77.35%   77.39%   +0.04%     
==========================================
  Files         296      296              
  Lines       53919    53939      +20     
  Branches     6382     6380       -2     
==========================================
+ Hits        41706    41741      +35     
+ Misses      11782    11656     -126     
- Partials      431      542     +111

Impacted Files	Coverage Δ
proxy/meta2v2_remote.c	79.75% <ø> (+1.51%)	⬆️
meta2v2/meta2_gridd_dispatcher.c	68.19% <ø> (ø)	⬆️
...ests/functional/content/test_content_versioning.py	100% <100%> (ø)
tests/functional/cli/container/test_container.py	98.25% <100%> (+0.1%)	⬆️
meta2v2/meta2_utils_lb.c	79.55% <0%> (-11.36%)	⬇️
oio/ecd/app.py	59.77% <0%> (-6.5%)	⬇️
meta2v2/meta2_utils_json_in.c	32.2% <0%> (-4.1%)	⬇️
sqliterepo/replication_dispatcher.c	48.05% <0%> (-3.51%)	⬇️
meta2v2/meta2_utils_json_out.c	95.56% <0%> (-3.33%)	⬇️
sqliterepo/sqlite_utils.c	84.79% <0%> (-1.44%)	⬇️
... and 29 more

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