ci: use github app for release-please permissions

[gustavkj]

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I noticed that we have an issue with the release PR made by release-please. Since events triggered by the Github Actions bot won't trigger additional runs, the status checks aren't met as the workflows won't run.

One way to fix this is to set up a Github App user for release-please to use, that way it is a different user and as such the workflows will trigger.

If we choose this option, you need to create a Github App:

1. Go to the app creation form and give it a relevant name, e.g. Codeowners-Generator Release Bot.
2. Untick Active under Webhook
3. Under Repository permissions set Contents: write and Pull-requests: write, which are the permissions that release-please needs.
4. Make sure Where can this GitHub App be installed? is set to Only on this account.
5. Click Create Github App
6. Generate a private key for the app.
7. Go to the secrets settings for this repo, create a secret named RELEASE_PLEASE_PRIVATE_KEY and set it to the content of the newly generated private key. Create another secret named RELEASE_PLEASE_APP_ID and set it to the App ID.
8. Last step is to install the app for the repo.

[coveralls]

Pull Request Test Coverage Report for Build 7488811828

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 6989677130:	0.0%
Covered Lines:	263
Relevant Lines:	263

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💛 - Coveralls

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (91bab21) 100.00% compared to head (a47b1e8) 100.00%. Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #396   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines          284       284           
  Branches        64        64           
=========================================
  Hits           284       284           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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[gagoar]

Thanks for the detailed steps. I will do this after we release these new functionalities.