Cleanup proto

[chacha912]

What this PR does / why we need it:

• Remove unnecessary client information from the protobuf response
• Change clientID type from bytes to string in the API
  • Only the actorID in changeID needs to be kept as bytes: Replace ActorID type with UUID or Long instead of String to reduce the size of CRDT meta #36
  • but, if clientID needs to be maintained as bytes, it's possible to revert the commit, so please let me know.

Which issue(s) this PR fixes:

Fixes #498

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

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

[hackerwins]

Is the change from using bytes to strings for ClientID in APIs due to consistency reasons? (There seems to be no size problem because they are not included in documents.)

[codecov]

Codecov Report

Merging #614 (76402cb) into main (b111ab1) will decrease coverage by 0.01%.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##             main     #614      +/-   ##
==========================================
- Coverage   50.24%   50.23%   -0.01%     
==========================================
  Files          69       69              
  Lines        7314     7305       -9     
==========================================
- Hits         3675     3670       -5     
+ Misses       3147     3145       -2     
+ Partials      492      490       -2     

Files Changed	Coverage Δ
client/client.go	13.48% <11.11%> (ø)
server/rpc/yorkie_server.go	56.86% <91.66%> (+0.03%)	⬆️

[chacha912]

@hackerwins Yes, your point is accurate. It would also reduce the need for frequent conversions between bytes and string during usage.