Activate liquidity baking

Context

Supersedes !2473 (closed)

Fixes #1238 (closed)

TZIP draft

Agora comments

Manually testing the MR

Build and run in sandbox. The CPMM and liquidity token contracts are originated during stitching along with a sample FA1.2 contract (in place of tzBTC).

The escape hatch can be invoked through a per_block_votes JSON file (that can be used for changing constants in a future upgrade), e.g. tezos-baker-alpha --votefile "per_block_votes.json" where per_block_votes.json contains {"liquidity_baking_escape_vote": true}.

Unit tests can be run with dune exec src/proto_alpha/lib_protocol/test/main.exe -- test "^liquidity baking$".

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, the Development Version section of CHANGES.md for everything else).
• Select suitable reviewers using the Reviewers field below.

Reviewers

@mbouaziz @rafoo_ @klakplok @ZaynahDargaye @tomjack @arvidnl @galfour @bsall