Visual countdown timer to start match

**Is your feature request related to a problem? Please describe.**
The countdown to start matches is currently completed verbally by the game announcer (or ref). This is an issue for accessibility for hard-of-hearing teams, and all participants and volunteers in a loud venue who may not be able to hear the game announcer clearly.

**Describe the solution you'd like**
Including an optional setting in the scorekeeping software to incorporate the countdown into the scorekeeping system.

When enabled, pushing "Start Match" launches a 3,2,1, Start sequence before beginning the Autonomous period.


**Describe alternatives you've considered**
A volunteer in the UK Championship had created a remote controlled light strip and cue book for a hard-of-hearing team. An API that allows other accessibility systems would be helpful but as the countdown is not present in the scorekeeping software still relies on another person to time the countdown correctly.

**Additional context**
An integrated countdown has the added benefit of reducing match start errors as the countdown triggers the start of the match rather than relying on the scorekeeper to start precisely on the game announcer's cue.

Start by tracing the scorekeeping software's "Start Match" flow and the transition into the Autonomous period, then locate where optional settings are handled. Done means an enabled setting shows a visual 3, 2, 1, Start sequence and triggers the match at the end, while the existing behavior remains unchanged when disabled.

Written by the indexing model from the issue text.