APPSRE-5046 generated types for service_dependencies

[fishi0x01]

We want to introduce saas_file_v2 in service_dependencies checks.

1. we add our new code generator to reconcile.
2. we include an introspection.json of our schema. That json is required in order to infer types. The json is generated by the code generator via make gql-introspection. Note, that at a later step we might decide to package the introspection schema in a different place/repo. This is the first iteration.
3. we place our gql query into a dedicated .gql file.
4. the code generator generates corresponding data classes via make gql-query-classes.
5. we migrate existing logic to use the new generated types

From now on, any schema change will also require:

make gql-introsprection
make gql-query-classes

If the schema is not compatible in any way, we will see errors during type checking phase.
A check that the introspection.json and generated classes are up-to-date with the latest schema should be part of CI in later step.

This will be merged after we merged our design doc for the code generator. Design doc is merged.

This PR gives a very practical insight on how type generation will look on an existing integration.

A follow-up PR will then introduce saas_file_v2 to the query.

[fishi0x01]

@geoberle brought up an interesting idea on slack: generating a convenience function to load the query string.

def load_query_string() -> str:
  with open('path_to_file.gql', r) as f:
    return f.read()

That way we dont have to mess around with the file paths. I will add this to the generator now.

[fishi0x01]

Convenience function to load query strings added here: app-sre/qenerate#21

I.e., @geoberle 's idea is implemented now

[chassing]

LGTM

[patjlm]

get_provision_providers seems to not be used anywhere anymore (except in a test file), can we remove it and clean the code further ?