Development versions of schemas

Schemas stored in src/ska_schemas/sdp/schemas are now allowed to have development versions by appending _dev to the end of the schema file name. If one wants to test such development version, they need to set the SKA_SCHEMAS_ALLOW_DEV_VERSION environment variable to True and use the schema as if it was a released version, e.g. version 2.0 only exists in dev form, in src/ska_schemas/sdp/schemas/v2_0_dev.py, then set it as follows to use it:

"interface": "https://schema.skao.int/ska-sdp-configure/2.0"