Update .gitignore

[PProfizi]

to prevent from pushing changes in gate, gatebin or grpc

• the .gitignore will prevent from committing new files
• the CODEOWNERS will force a review from integration proxies when these files are modified in a PR

Trying to find a way to automatically remove changes for these folders from the git stage.
ATM I think the required steps are:

• stash changes to these specific folders -> can be part of the pre-commit hooked tasks
• commit
• unstash/apply stash back to the working directory -> requires to set a post-commit hook

[codecov]

Codecov Report

Merging #1137 (d8272b0) into master (2c7f4bf) will increase coverage by 1.16%.
The diff coverage is n/a.

❗ Current head d8272b0 differs from pull request most recent head 12a66db. Consider uploading reports for the commit 12a66db to get more accurate results

@@            Coverage Diff             @@
##           master    #1137      +/-   ##
==========================================
+ Coverage   86.10%   87.26%   +1.16%     
==========================================
  Files          81       81              
  Lines        9197     9197              
==========================================
+ Hits         7919     8026     +107     
+ Misses       1278     1171     -107