Memory usage monitoring metrics

[jacob314]

See
#8120
Step 4 which is the in-progress code to implement this.
We need memory usage monitoring to catch when a Gemini CLI release introduces significant memory leaks and bloat.
The most important thing is we need to track memory usage after the app has been used a while rather than just memory usage on startup.

[jacob314]

Assigning as a contributor is landing.

[jacob314]

#8122 is landing now
Once this is landed a follow on PR still needs to enable it (steps 5 and 6 in the chain mentioned on the pr).

[jacob314]

8122 has landed. I believe we still need a follow up PR to enable the metrics.

[jacob314]

Next pr out for review as well