Offchain Governance Metadata

[Cmdv]

Currently we are storing the whole of the json into the Database inside of OffChainVoteDataJson / offchainvote table
which happens around here:

cardano-db-sync/cardano-db-sync/src/Cardano/DbSync/OffChain.hs

Lines 115 to 118 in c5d6b8a

	insert :: (MonadBaseControl IO m, MonadIO m) => OffChainPoolResult -> ReaderT SqlBackend m ()
	insert = \case
	OffChainPoolResultMetadata md -> void $ DB.insertCheckOffChainPoolData md
	OffChainPoolResultError fe -> void $ DB.insertCheckOffChainPoolFetchError fe

current functionality was introduced in this PR

TLDR currently we:

1. fetch offchain metadata
2. put it into DB inside OffChainVoteDataJson

What we'd ideally like is:

1. fech offchain metadata
2. parse metadata
3. put parsed metadata into a new table with same structure as the parsed type
4. link newly created row id in OffChainVoteDataJson which is currently of the typeText

We can get the expected structure from cardano-foundation/CIPs#632 once it is merged and finalised.

[kderme]

An initial implementation of this is done at sancho-4-1-0