Allow message deletion policies to be configured globally.

While we have the ability to configure team chats to automatically delete messages after an interval, it would be nice if one could set this policy globally for all chats.

For example, it looks like I am able to set a a deletion policy on a per chat basis outside of teams. Please allow this to be configured as a default so that all new chats are set to automatically delete based on the configured policy. :D

No file or test is named. Start by tracing the existing team-chat automatic deletion policy and the per-chat policy path, then identify where their defaults are stored and applied. Done means a configured global default applies to all new chats while per-chat policies remain available, with coverage for the resulting configuration.

Written by the indexing model from the issue text.