docs: Changelog & bug template for 2.13.0 release

[wozniakjan]

Preparing changelog and bug template for 2.13.0 release

Checklist

• Commits are signed with Developer Certificate of Origin (DCO - learn more)

Relates to #5275

[wozniakjan]

taking #5015 as a template

[github-actions]

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While you are waiting, make sure to:

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[github-actions]

Thank you for your contribution! 🙏 We will review your PR as soon as possible.

While you are waiting, make sure to:

• Add an entry in our changelog in alphabetical order and link related issue
• Update the documentation, if needed
• Add unit & e2e tests for your changes
• GitHub checks are passing
• Is the DCO check failing? Here is how you can fix DCO issues

Learn more about:

• Our contribution guide

[wozniakjan]

The last desired PR has merged - #4628. Opening this for reviews.

ptal @kedacore/keda-core-contributors, I think the test failure is a flake

[It] shouldn't validate the so creation when the replica counts are wrong
/__w/keda/keda/apis/keda/v1alpha1/scaledobject_webhook_test.go:146

[tomkerkhove]

/skip-e2e