doc: describe validator state machine

[redshiftzero]

After #32 and #73 we will have implemented the full validator state machine we'll use for any production use of this chain. We should document how it works in docs.webcat.tech so it's legible to folks who are reviewing changes or debugging prod issues.

We should cover:

• The four states described in validator: status tracking, jailing, tombstoning, automatic unjailing #135
• The 8 transitions between states and where they get handled in the system
• The two levels of power in the system: BASE_VALIDATOR_POWER, 1, 0 and why we did this (so we can automatically unjail)
• The bitvec-based uptime tracker
• The deadband approach for jailing / unjailing (unjail_missed_max and missed_blocks_max)