Loose enforcement of OpenAPI compatibility

[jpraynaud]

Why

Currently if the minor version of the OpenAPI is bumped, all the previous versions of the signer, client and aggregator will fail to retrieve information from an updated aggregator. This is due to the aggregator which strictly enforces the compatibility of the versions of OpenAPI between the nodes.

What

Replace the strict OpenAPI verification mechanism with a loose one.

How

• Do not reject a request made by a client running a possibly incompatible version of the OpenAPI in the aggregator
• In the aggregator client display a warning message when versions looks incompatible:
  • In the signer
  • In the aggregator (when follower)
  • In the client library