docs: add links and updates to whats new 7.0 (#24715)

* docs: add links and updates to whats new 7.0

* Apply suggestions from code review

Co-authored-by: Jessica <4947705+jessabe@users.noreply.github.com>
Co-authored-by: Carl Bergquist <carl@grafana.com>

* Update docs/sources/guides/whats-new-in-v7-0.md

Co-authored-by: Jessica <4947705+jessabe@users.noreply.github.com>

* docs: link for time zones in what's new

* Backend plugins update

Co-authored-by: Jessica <4947705+jessabe@users.noreply.github.com>
Co-authored-by: Carl Bergquist <carl@grafana.com>
Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>