GCD utilization in Timeline

[Adamrch]

Is your feature request related to a problem? Please describe.
When I am working on creating a new rotation APL or modifying an existing one it is difficult to see if my conditions are wasting too much free GCD time. I would like to know if there are big periods of low GCD usage.

Describe the solution you'd like
Add a bar in Timeline that shows Blue when on-gcd and nothing for off GCD. (for the 1 iteration)
Under casts add a GCD Utilitzation section with metric Time Spent out of GCD, and GCD Utilization which is time spent in GCD divided by the encounter length. (for a average summary of all iterations)
I am not a caster, but I imagine for them you can include cast time and channeling time in those metrics.

Describe alternatives you've considered
Not really sure what else would help

Additional context
N/A