Spacing of oracle reports by reacting to on-chain events

[yerdua]

Expected Behavior

"I think to make it truly robust, we'd want to listen for events that say an oracle was added or removed, or the bucket update frequency has changed." -- Audrey

When certain on-chain events happen, the oracle should recalculate the timing of its reports to preserve ideal spacing.
These events include changes to anything that is used to derive configuration of the oracle.

Current Behavior

During initialization, in both the timer-reporter and the block-based-reporter, the oracle will figure out when to report, spaced out from the other oracles. This calculation only happens during initialization though, so if other oracles are added or removed after this, it could lead to non-ideal spacing, or multiple oracles trying to report in the same block.