Setup OpenAPI merger

[robcxyz]

We need to combine all the OpenAPI docs into one from https://tracker.icon.community/ > tools > api docs > All of these... All the endpoints are already in the initial PR commit

Branch: https://github.com/sudoblockio/icon-stats/tree/openapi-merger
PR: #7 -> See PR for files relating to this feat.

Bring over the merger from https://github.com/sudoblockio/sb-pocs/blob/main/apisix/openapi_merger

Most has been just copied over but missing main.py which should not be needed because code is called from API with a cache. https://github.com/sudoblockio/icon-stats/blob/openapi-merger/icon_stats/api/v1/endpoints/openapi.py

There are five endpoints which should be the input to the merger. The merger in the POC is a CLI and so basically the code in the icon_stats/openapi dir will hopefully be generic so that it can be reused later. Not a huge priority now though as we just need to ship the merger for the grant.

Test should make the calls and validate the inputs. Might need to pull out logic from API so that this is more testable (ie the endpoints / endpoint_suffixes stuff). Don't need to test the API directly.