Upgrade Squid to work with parachain 1.21.0

[bvotteler]

As part of issue #35 we need to be able to run squid on runtime version 1021000.

Docker images are available to run the parachain locally and get the metadata through that for typegen.
(parachain image name: interlayhq/interbtc:1.21.0, clients version 1.19.0)

[bvotteler]

For (future) reference, notes on how to manually merge types from various chains:

1. Save mainnet versions into chainVersions.jsonl with squid-substrate-metadata-explorer(1) - https://github.com/subsquid/squid-sdk/blob/ab1cae1eb6c9c4a34760f4fea09dff45c2f4065b/substrate/substrate-metadata-explorer/README.md
2. Save testnet versions into a separate file with the same tool
3. Copy testnet versions into a main file, possibly adjusting .specName, .specVersions fields as needed.
   • specName in particular should have same name otherwise generation creates isV names some with specName in it
4. Just pass the resulting file to a typegen

This preserves the "old" versions that are present on mainnet chains.