Improve instruction workflow to activate bridges

Originally created by @sajolida on #10280 (Redmine)

Bridges are explained in /first_steps/startup_options/bridge_mode but the “How to use bridges in Tails” on this page doesn’t actually explain how to do that but rather points to /first_steps/startup_options/network_configuration. We could use an inline to insert the relevant content in both places.

Feature Branch: doc/10280-bridge-activation-workflow

Related issues

• Blocks #9752 (closed)