FA2 support + Proto H

Add support for FA2 and token discovery, with changed/new RPCs:

• /accounts/<address>/operations now corresponds to the previous .../next
• /tokens/registry returns the list of every tokens and their standard (fa1-2 or fa2). It can be filtered using ?accounts=<address1>,<address2>,... to retrieve only the tokens relevant for a set of accounts.
• /accounts/<address>/tokens returns the set of tokens relevant for an account. It is equivalent to tokens/registry?accounts=<address>
• /tokens/exists returns "fa1-2", "fa2" or null instead of a boolean.

Some RPCs have been removed, since they are no longer used in Umami:

• /tokens, in favor of /tokens/registry
• /accounts/<address>/tokens/<kt1>:
  • /balance (Umami uses tzip4 run_view from octez 10)
  • /operations (integrated into the multikind operations from a previous MR)
• /accounts/<address>/operations/next

Also adds support for proto H.

I'll draft the MR until we can set a proper docker image reference for tezos_indexer.