feat: Extend changelog generation to show release note category and target_group

[moelsayed]

What this PR does / why we need it:
Extends change log generation to show release note category and target_group from the pull request template.

Which issue(s) this PR fixes:
Fixes #openmcp-project/backlog#176

Special notes for your reviewer:
For example, the release v0.9.1 for the openmcp-operator looks like this:

# Changes included in v0.9.1:

### 🐛 Fixes
- fix wrong reference type in Cluster type [#90](https://github.com/openmcp-project/openmcp-operator/pull/90).

With the changes in this PR, it would look like this:

# Changes included in v0.9.1:

### 🐛 Fixes
- [bugfix] [dependency] fix wrong reference type in Cluster type [##90](https://github.com/openmcp-project/openmcp-operator/pull/90): Fixed a bug in the cluster config references of the `Cluster` type that required a namespace to be specified. The references must always refer to cluster configs in the same namespace as the referencing Cluster, setting a namespace is therefore neither required nor allowed.

Release note:

The change log generation process now shows release note category and target_group from the pull request template.