[MMR] production ready Merkle Mountain Range pallet (and gadget)

[acatangiu]

The Vision

Have an on-chain MMR capable of following chain progress and capable of proving some customizable leaf data is part of the chain.

Requirements

• Minimal on-chain data,
• Full MMR contents should go to offchain db and should be optional for nodes,
• Any node can verify proofs,
• Generating proofs can be done only by nodes that opted in saving full MMR offchain.

The Plan

• MMR leaves in off-chain storage can be overwritten by forks grandpa-bridge-gadget#336
• MMR Proof Generation is broken substrate#11984
• pallet-mmr: batch proofs are sometimes broken substrate#11753
• pallet-mmr: Change runtime API and RPC API to work with block numbers instead of leaf indices substrate#12339
• pallet-mmr: improve offchain storage, relax LeafData requirements substrate#11799 <-- (attempts to do it failed, dropping it)
• zombienet: add test for BEEFY and MMR RPCs substrate#11972
• pallet-mmr: move offchain logic to client-side gadget substrate#12508
• pallet-mmr: gate MMR offchain canonicalization behind --enable-offchain-indexing=true substrate#12531
• client/mmr: make it resilient to finality notifications loss substrate#12780
• mmr: move RPC from frame to client substrate#12804
• MMR Leaf Data: off-by-one error in beefy_next_authority_set substrate#11797
• mmr proof generation failures on rococo substrate#12864

Integration

• Deploy and test all the above on Rococo

[acatangiu]

This is complete