Make Provider multichain

[calina-c]

Works on #572

Pending TODOs:

• test functions for env var decoding, fallbacks etc.
• return c2d environments indexed by chainId instead of flat list
• update c2d and remove chainId from status, stop and delete payloads
• run a full pre-commit script on all files to fix issues that were allowed during the development phase

[LoznianuAnamaria]

Moved the testing part of Multichain Provider to this issue: #591

[mihaisc]

@calina-c can you please do a rebase so we can test this