Add feature flag to reduce debounce time

[philipp-spiess]

Closes CODY-1533

Gives us back one of the few (only?) client-side lever we still have for latency. When this feature flag is on, we only have a 25ms debounce time (as we did in our initial versions). Note that this will also increase backend pressure and load when enabled, which might have a negative impact on latency too.

Test plan

• Enable the cody-autocomplete-reduced-debounce feature flag (I did it by patching the source code but you can also connect to sg locally and enable it in the instance)
• Trigger a completion and notice slightly faster completions. I enabled tracing for me and checked out a trace.