feat(manager/fleet): implement Rancher Fleet manager (#16138)

* feat(manager/fleet): implement Rancher Fleet manager

* Apply suggestions from code review

Co-authored-by: HonkingGoose <34918129+HonkingGoose@users.noreply.github.com>

* Update lib/modules/manager/fleet/extract.spec.ts

Co-authored-by: Michael Kriese <michael.kriese@visualon.de>

* docs(fleet): add tsdocs

* fixup test null checks

* docs: add default filematch

* chore: rename tempDep to dep

* apply change requests

* catch exceptions from yaml-js

* trigger yaml parse error

Co-authored-by: HonkingGoose <34918129+HonkingGoose@users.noreply.github.com>
Co-authored-by: Michael Kriese <michael.kriese@visualon.de>