Introduce Gnocchi helm chart to Genestack

[LukeRepko]

This PR introduces helm configs for Gnocchi (OpenStack Metrics API) and its dependency, PostgreSQL. Gnocchi is a dependency of Ceilometer, which we will be adding to Genestack soon.

Note that PostgreSQL is being used as the indexer storage back-end in favor of our existing MariaDB operator implementation for several reasons.

1. Gnocchi cites PostgreSQL as the preferred driver (though they don't state why exactly).
2. I could not get the MySQL driver working with the helm chart, despite several attempts. It seems like it may be possible, but instructions are unclear, and there may be a bit of overhaul with the chart required to get it to work as expected. MySQL is supported by Gnocchi though, so it's within the realm of possibility.

Iff we go with PostgreSQL long term, we will want to investigate the upstream operator. The existing chart works and is being maintained to some extent, but the operator no doubt has more active contributors and will likely suit Genestack better.

[LukeRepko]

Not ready for merge just yet, will be following up with one or two more commits to add documentation where appropriate regarding installing postgresql and gnocchi.

[LukeRepko]

Getting a 403 from the Gnocchi API pod over its service port 8041 -- looks like apache is denying requests due to...

[Tue Mar 05 20:19:45.567830 2024] [authz_core:error] [pid 8:tid 140141779719936] [client 10.233.64.50:40838] AH01630: client denied by server configuration: /var/lib/kolla/venv/lib/python2.7

That path doesn't exist because.... we have python3.x now. There is a place to update the apache configuration in the gnocchi-helm-overrides.yaml -- doing so now.

[LukeRepko]

Past the previous issue, now getting a 500 response. There's a traceback in the gnocchi api logs related to there not being a section for gnocchi+keystone within /etc/gnocchi/api-paste.ini (which is derived from the helm-config-overrides). There's an updated api-paste in gnocchi/rest/ -- investigating.

[LukeRepko]

Getting a 200 finally:

curl -D - -sH "x-auth-token: $token" http://gnocchi-api.openstack.svc.cluster.local:8041/healthcheck
HTTP/1.1 200 OK
Date: Wed, 06 Mar 2024 01:24:12 GMT
Server: Apache/2.4.41 (Ubuntu)
Content-Length: 0
Vary: Accept-Encoding
Content-Type: text/plain; charset=UTF-8

Note: Looking at the version response, the build is 4.4.4. The gnocchi_api image being used is quay.io/openstack.kolla/ubuntu-source-gnocchi-api:yoga - built only about a month ago. Gnocchi is up to 4.6.1, so this is pretty far behind.

ubuntu@openstack-flex-node-0:~$ curl -sH "x-auth-token: $token" http://gnocchi-api.openstack.svc.cluster.local:8041/ | jq
{
  "build": "4.4.4",
  "versions": [
    {
      "status": "CURRENT",
      "links": [
        {
          "rel": "self",
          "href": "http://gnocchi-api.openstack.svc.cluster.local:8041/v1/"
        }
      ],
      "id": "v1.0",
      "updated": "2015-03-19"
    }
  ]
}```

[cloudnull]

A couple nits, and one general question.

Additionally, it looks like we're following openstack-helm's deployment of postgres, could we use the upstream postgres operator? https://postgres-operator.readthedocs.io/en/latest/

[cloudnull]

LGTM