Support Oasis Scan API v2

[buberdds]

https://api.oasisscan.com/v2/swagger/

TODOs:

• [ ] runtime query param will be added to V2 transactions endpoint in the future. At this point we cannot show ParaTime deposits or withdraws https://github.com/bitcat365/oasisscan-backend/issues/8
• [ ] debug why generated API files had to be updated manually
• [ ] define tx method enum in swagger (issue created in bitcat repo or patch in repo)
• [x] issue with spec vs API type mismatch https://github.com/bitcat365/oasisscan-backend/issues/9
• [x] incorrect swagger spec https://github.com/bitcat365/oasisscan-backend/issues/7#event-14823468676
• [x] define Allowance enum in swagger https://github.com/bitcat365/oasisscan-backend/issues/10#event-14853377973

Notes:

• tx amount is not rounded anymore in API
• we can extract common helpers for v1 and v2, but at the end v1 will be removed completly

[github-actions[bot]]

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