[raft] Possible optimizations

[the-glu]

This PR shows a few possible optimizations for raft.

It should be split into dedicated PRs when parent PRs are merged, to be compatible with the latest version of the code.

Optimizations are:

• Proposals encoded with a simple encoder
• Optional compression of proposals above a specific threshold
• Smaller encoding of known ovn formats
• Removal of extra information in upsertOperationalIntentReference, moving cells computation into transaction + removing useless keys

This greatly improves performance with latency (around 10x with flightsinsub and 33ms of latency).