Migrate from Flask to FastAPI (#163)

* Migrate from Flask to FastAPI

 * FastAPI migration:
    - Use pydantic model classes as input parameters to the
      data/calculation classes.
    - Interface field names changed to constructor parameter names (for
      simplicity only during transition, should be updated in a followup
      PR).
    - Add basic interface requirements (e.g. some values > 0, etc.).
 * Update tests for new data format.
 * Python requirement down to 3.9 (TypeGuard no longer needed)
 * Makefile: Add helpful targets (e.g. development server with reload)

* Move API doc from README to pydantic model classes (swagger)

 * Link to swagger.io with own openapi.yml.
 * Commit openapi.json and check with pytest for changes so the
   documentation is always up-to-date.

* Streamline docker

* FastAPI: Run startup action on dev server

 * Fix config for /strompreis, endpoint still broken however.

* test_openapi: Compare against docs/.../openapi.json

* Move fastapi to server/ submodule

 * See #187 for new repository structure.

tests/conftest.py

@@ -50,7 +50,7 @@ def server(xprocess, tmp_path: Path):
         # assure server to be installed
         try:
             subprocess.run(
-                [sys.executable, "-c", "import akkudoktoreosserver"],
+                [sys.executable, "-c", "import akkudoktoreos.server"],
                 check=True,
                 stdout=subprocess.PIPE,
                 stderr=subprocess.PIPE,
@@ -65,11 +65,11 @@ def server(xprocess, tmp_path: Path):
             )
 
         # command to start server process
-        args = [sys.executable, "-m", "akkudoktoreosserver.flask_server"]
+        args = [sys.executable, "-m", "akkudoktoreos.server.fastapi_server"]
         env = {EOS_DIR: f"{tmp_path}", **os.environ.copy()}
 
         # startup pattern
-        pattern = "Debugger PIN:"
+        pattern = "Application startup complete."
         # search the first 30 lines for the startup pattern, if not found
         # a RuntimeError will be raised informing the user
         max_read_lines = 30
@@ -81,14 +81,14 @@ def server(xprocess, tmp_path: Path):
         terminate_on_interrupt = True
 
     # ensure process is running and return its logfile
-    logfile = xprocess.ensure("akkudoktoreosserver", Starter)
+    logfile = xprocess.ensure("eos", Starter)
 
     # create url/port info to the server
     url = "http://127.0.0.1:8503"
     yield url
 
     # clean up whole process tree afterwards
-    xprocess.getinfo("akkudoktoreosserver").terminate()
+    xprocess.getinfo("eos").terminate()
 
 
 @pytest.fixture