Configurable timer durations

[tilacog]

The Agent has numerous timed, cyclic operations with hard-coded durations, but indexers may want to customize their frequency.
Therefore, exposing those timer durations in configuration would be beneficial.

We can use the current, hard-coded durations as a default for all timers.

[tilacog]

I'd suggest putting those new options under the indexerOptions section of the network specification files so each network can have its preferences.