Add subtrate support to API

[freddyli7]

Expand fee oracle API to support fee data requests where the destination chain is a substrate-based chain with deployed Sygma pallet.

Implementation details

• Details of fee data message format can be found in technical documentation (will be available after this PR is merged)
• API endpoint handler function should be expanded so it takes into consideration the destination domain (network) type when constructing a response
• Additional query property should be supported (length_fee) when the user requests a generic call fee estimate with the substrate-based destination chain.

Testing details

• Add unit test

Acceptance Criteria

• Fee Oracle should return appropriate fee data when requested for the destination chain being substrate-based

[P1sar]

@MakMuftic I have updated the task for Solidity changes
https://app.zenhub.com/workspaces/sygma-protocol-62f126a54b7d5a55203732f0/issues/gh/sygmaprotocol/sygma-solidity/60
There are some details regarding the implementation on the soldidity side.
Generally I put notes from the buttom of this document that we were discussing.
Please also check if that is correlates with what you know.