server/app/interfaces/repository.py: Implement missing `/serialization` endpoint

[moritzsommer]

Current Situation

Currently, server endpoint /serialization", methods=["GET"], endpoint=self.not_implemented is not implemented.

According to the AAS Repository Service OpenAPI Specification, the endpoint should return a serialisation of selected AASs and Submodels.

[...]
summary: Returns an appropriate serialization based on the specified format (see SerializationFormat)
[...]
responses:
  '200':
    description: Requested serialization based on SerializationFormat
    content:
      application/asset-administration-shell-package+xml:
        schema:
          description: AASX package
          type: string
          format: binary
      application/json:
        schema:
          $ref: 'https://api.swaggerhub.com/domains/Plattform_i40/Part1-MetaModel-Schemas/V3.0.1#/components/schemas/Environment'
[...]

This issue specifies #439.

Proposed Chang

We should evaluate and, if feasible, implement GET /serialization according to the specification.

[zrgt]

Assigned to @thammel