As a Quay administrator,
I want to be able to mark certain fields in Quay's config app as read-only,
So that it will be clear to other administrators that certain fields are managed outside of the config app.

Changes:

• When launching the configuration app, the environment variable CONFIG_READ_ONLY_FIELDS is used to determine if fields should be marked as read-only in the User Interface.
• The following sections in the configuration app can be marked as read-only: redis, hostname

Acceptance Criteria

• Run the configuration app without the new environment variable. It should work normally and all fields should be modifiable.
• Run the configuration app without the new environment variable. Modify an existing Cluster's configuration. All fields should be modifiable.
• Run the configuration app with the environment variable CONFIG_READ_ONLY_FIELDS=redis,hostname. Modify an existing cluster configuration. The redis section and "server configuration" (hostname) sections should be marked as read-only with an appropriate message.
• Run the configuration app with just one of the option. Modify an existing cluster configuration. The one that isn't marked, should be editable. The one that is marked should be read-only.