Internal operation manual to recover chain finality and bridge-grandpa after granpa stalled.

[hackfisher]

Generally, there could be several key steps:

• Send grandpa.note_stalled to force recover the chain's grandpa finality.
• For bridge's bridge-grandpa pallet, since the grandpa authorities are reset, we need to kill and clean the bridge-granpa pallet's storage for the next re-initialization.
• Bridge re-initialization.

We need more tests for the reinitialization and a wiki to draft more details for the operation manual guide for devs to follow step by step when undesired things happen.