feat(manager/crossplane): add Crossplane xpkgs support (#25896)

lib/modules/manager/api.ts

...les/manager/crossplane/__fixtures__/malformedPackages.yml

...modules/manager/crossplane/__fixtures__/mixedManifest.yml

...odules/manager/crossplane/__fixtures__/randomManifest.yml

...modules/manager/crossplane/__fixtures__/validPackages.yml

lib/modules/manager/crossplane/extract.spec.ts

lib/modules/manager/crossplane/extract.ts

lib/modules/manager/crossplane/index.ts

lib/modules/manager/crossplane/readme.md

lib/modules/manager/crossplane/schema.ts