Add additional headers to the release notes tool output

[mjlshen]

As mentioned in #9104,

In recent releases, there are some additional header sections that have been manually generated, such as "Highlights" and "Deprecation Warning" - these should be automatically generated by the release notes tool even if the content is not automated, a template with placeholders is fine.

Release notes tool: https://github.com/kubernetes-sigs/cluster-api/blob/main/hack/tools/release/notes.go

[mjlshen]

/assign

[furkatgofurov7]

/triage accepted

[furkatgofurov7]

Based on the agreement during the call triaging #9104, setting the priority to:

/priority important-soon