Add logout command to CLI

[blurfx]

What this PR does / why we need it: Add logout command to yorkie cli

Which issue(s) this PR fixes:

Fixes #488

Special notes for your reviewer:

Since yorkie login allows login to multiple servers, logout should also allow logout on a per-server basis. thus yorkie logout command would work as follows:

• If the user is logged in to only one server
  • can log out with yorkie logout.
• If the user is logged in to multiple servers
  • can log out from a specific server with yorkie logout --rpc-addr "<SERVER_ADDRESS>".
• or log out from all servers with yorkie logout --force. (is --all is better name than --force?)

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Merging #571 (5b6446e) into main (3e34fc6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #571   +/-   ##
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  Coverage   51.31%   51.31%           
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  Files          67       67           
  Lines        6949     6949           
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  Hits         3566     3566           
  Misses       2915     2915           
  Partials      468      468           

[hackerwins]

Thanks for your contribution.