Add memstat flag

[GuessWhoSamFoo]

What this PR does / why we need it:
Allows users to benchmark memory usage without needing additional setup

Which issue(s) this PR fixes

• related to Even when doing nothing, Octant burns cpu cycles #2013

Special notes for your reviewer:
Command can be invoked by:
octant --disable-open-browser --memstats stats.txt --meminterval 500ms

then observe via tail -f stats.txt

Signed-off-by: Sam Foo foos@vmware.com

[wwitzel3]

Thanks, this is useful. In the future lets think about how we can start to expose these knobs easily through our preferences. We have a developer section that can have flags like this.