feat: add GitHub App authentication support

[erka]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 72.28916% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.68%. Comparing base (17ed13d) to head (1e73c0d).

Files with missing lines	Patch %	Lines
internal/credentials/credentials.go	70.49%	14 Missing and 4 partials ⚠️
internal/storage/environments/environments.go	0.00%	4 Missing ⚠️
...nal/coss/storage/environments/git/github/github.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##               v2    #5327      +/-   ##
==========================================
+ Coverage   60.53%   60.68%   +0.15%     
==========================================
  Files         138      138              
  Lines       13540    13606      +66     
==========================================
+ Hits         8196     8257      +61     
- Misses       4653     4654       +1     
- Partials      691      695       +4     

Flag	Coverage Δ
integrationtests	34.44% <0.00%> (-0.18%)	⬇️
unittests	51.99% <72.28%> (+0.19%)	⬆️

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[github-actions]

👋 Hi @erka! Thanks for your contribution to this project.

It looks like one or more of your commits are missing a DCO (Developer Certificate of Origin) sign-off. The DCO is a simple way for you to certify that you have the right to submit this code under the project's license.

How to fix this:

# For future commits, use the -s flag
git commit -s -m "Your commit message"

# To sign off on existing commits in this PR
git rebase HEAD~$(git rev-list --count origin/v2..HEAD) --signoff
git push --force-with-lease

The -s flag adds this line to your commit message:
Signed-off-by: Your Name <your.email@example.com>

📋 View the failing DCO check for more details

For more information about the DCO, visit: https://developercertificate.org/

[github-actions]

👋 Hi @erka! Thanks for your contribution to this project.

It looks like one or more of your commits are missing a DCO (Developer Certificate of Origin) sign-off. The DCO is a simple way for you to certify that you have the right to submit this code under the project's license.

How to fix this:

# For future commits, use the -s flag
git commit -s -m "Your commit message"

# To sign off on existing commits in this PR
git rebase HEAD~$(git rev-list --count origin/v2..HEAD) --signoff
git push --force-with-lease

The -s flag adds this line to your commit message:
Signed-off-by: Your Name <your.email@example.com>

📋 View the failing DCO check for more details

For more information about the DCO, visit: https://developercertificate.org/