Add ansible Galaxy remote type (#137)

ansible-galaxy installs pull collections straight from galaxy.ansible.com because artifactapi has no Galaxy remote type.

- add `ansible` package type proxying the Galaxy v3 API (discovery, collection versions, artifact downloads)
- forward digits-only `limit` (capped at 100) and `offset` on metadata paths, canonicalised; tarball paths forward no query
- rewrite only `href`, `download_url` and `links.*` to root-relative remote paths so tarballs flow through artifactapi
- treat `artifacts/*.tar.gz` as immutable and JSON metadata as mutable
- add `docs/ansible/remote.md`, a UI type def and an ansible e2e caching case

requires unkin/artifactapi#146

Reviewed-on: #137
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

e2e-docker/caching_ansible_test.go

@@ -0,0 +1,7 @@
+//go:build dockere2e
+
+package e2edocker
+
+func init() {
+	cachingCases = append(cachingCases, cachingCase{"ansible", "galaxy/artifacts/ns-col-1.0.0.tar.gz", "galaxy/artifacts/ns-col-1.0.0.tar.gz"})
+}