Emit metrics for Actor reminder and timer

[artursouza]

In what area(s)?

/area runtime

/area operator

/area placement

/area docs

/area test-and-release

Describe the feature

Emit metrics for Actor reminder and timer being registered, deleted and fired

Release Note

RELEASE NOTE:

[filintod]

@artursouza do we need one metric for number of creates and one for number of deletes? or just a metric with total number is fine (going up and down)? Meaning do we need to add 3 metrics (total, delete/create and fire) for reminders and timers or just 2 (total and fired) is enough?

[filintod]

/assign

[artursouza]

@artursouza do we need one metric for number of creates and one for number of deletes? or just a metric with total number is fine (going up and down)? Meaning do we need to add 3 metrics (total, delete/create and fire) for reminders and timers or just 2 (total and fired) is enough?

I am inclined to just have total and fired.