Support using PR title instead of commit heading when generating changelogs and release notes

**Is your feature request related to a problem? Please describe.**

In our repository, we enabled automated dependency updates using tools such as Dependabot and Renovate Bot. These tools create PRs with titles that have details about the versions of dependencies being updated. The heading of commit messages in those PRs are shorter to (try to) make them compliant with the Conventional Commits spec when they might overflow a certain length.

As release-please pulls the commit title to write it in the changelog and in release-notes, it might obfuscate the version information.

Example:

PR title: `deps(docker): bump dotnet/sdk from 8.0.302-alpine3.20 to 8.0.303-alpine3.20`
Commit heading: `deps(docker): bump dotnet/sdk`
Commit description:

```
Bumps dotnet/sdk from 8.0.302-alpine3.20 to 8.0.303-alpine3.20.

---
updated-dependencies:
- dependency-name: dotnet/sdk
dependency-type: direct:production
update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot]
```

Resulting changelog and release notes line: `docker: bump dotnet/sdk (link to PR) (link to commit)`

**Describe the solution you'd like**

A configurable option to use the PR title instead of the commit heading to generate the changelog and the release notes.

Desired changelog and release notes line: `deps(docker): bump dotnet/sdk from 8.0.302-alpine3.20 to 8.0.303-alpine3.20 (link to PR) (link to commit)`

**Describe alternatives you've considered**

[Manually rewriting](https://github.com/googleapis/release-please/blob/main/README.md#how-can-i-fix-release-notes) release notes might be an option, although it doesn't scale.

**Additional context**

Nothing for now.

Thanks for your support!