Flagging Active and Inactive Mailing Lists

Some of the older ASF mailing lists are no longer in use and are only there for display purposes. In theory would we not want to allow users to start any new threads or have users request subscriptions to them.

This enhancement is to look at adding a flag to a mailing to indicate if the list is active (e.g. allowing new posts and subscription requests) or inactive (not allowing new posts or subscription requests).

- If the list is active then the standard buttons to start a new thread, subscribe or unsubscribe to the list are displayed.
- If the list is inactive instead of displaying the standard buttons for starting a new thread or subscribing, a message could be displayed saying that posts and subscriptions to the list are closed for the list.

Start by tracing how mailing-list metadata is stored and how the new-thread, subscribe, and unsubscribe controls are rendered and handled. Determine the entry points for displaying a list and submitting those actions, then verify that active lists retain the standard controls while inactive lists show the closure message and reject new posts or subscription requests.

Written by the indexing model from the issue text.