Add option to read openapi schemas

[ondrej-ivanko]

Hi,

I was trying yours and openapi-tui and I was surprised that there is no option to read autogenerated or static openapi schema in your tool.

I'm using fastapi, which generates schema dynamically on API start and which is accessible on localhost:port/openapi.json. I would like to have option to read this schema and have it loaded under default collection name.

Later the collection can be renamed according the users needs. I think this saves user a lot of work from creating new collections.

Otherwise great tool. Thank you.