feat: use generic fog provider for external blobstore

[jandubois]

This PR implements 2 features:

• Generalize external blobstore support to S3 compatible endpoints, to Google and Azure cloud storage.
• Configure Eirini to use external blobstore.

The PR removes the old "s3" provider and replaces it with "fog" which provides a superset of capabilities. The JSON schema will make sure that attempts to use "s3" will get an error.

This PR supports the simple configurations from https://docs.cloudfoundry.org/deploying/common/cc-blobstore-config.html (specifying provider, keys, and bucket names), plus some extra settings for non-AWS versions of S3 compatible storage. Things like encryption or service accounts etc. are not implemented, as they all would require mapping for bits-service/eirini. Plain webdav is also not supported, except via the singleton-blobstore.

This PR has been tested with a recent local MinIO server, using both path style addressing (Diego) and vhost addressing (Eirini):

  blobstore:
    provider: fog
    fog:
      connection:
        provider: AWS
        aws_access_key_id: MY-KEY-ID
        aws_secret_access_key: MY-SECRET-KEY
        region: ""
        aws_signature_version: '2'
        endpoint: http://minio.home:9000
        # path_style: true

      app_package_directory_key: cap-staging-blobstore-packages
      buildpack_directory_key: cap-staging-blobstore-buildpacks
      droplet_directory_key: cap-staging-blobstore-droplets
      resource_directory_key: cap-staging-blobstore-resources

Fixes #1540

[jandubois]

Requires cloudfoundry-incubator/quarks-operator#1220 to be able to store fog_connection details in a secret instead of inlining them in an ops config map.

[mook-as]

Suggested change

	# endpoint: S3-ENDPOINT
	# endpoint: https://custom-s3-endpoint.example.com/

Or whatever the correct syntax is (to show what the correct syntax is).

[mook-as]

👍👍👍