adding fastapi server and add it to the vulndb command line

[fkautz]

Initial endpoints are:

@app.get("/"): Root endpoint that returns a status object.
@app.get("/cve/id/{cve_id}"): Endpoint to retrieve a CVE entry by CVE ID.
@app.get("/cpe/id/{cpe_id}"): Endpoint to retrieve a CPE entry by CPE ID.
@app.get("/osv/id/{id}"): Endpoint to retrieve an OSV entry by an ID or alias.
@app.post("/osv/purl"): Endpoint to retrieve an OSV entry by a Package URL (purl).
@app.post("/cve/purl"): Endpoint to retrieve a CVE entry by a Package URL (purl).

There is also an auto-generated /docs endpoint.

As a future item, if we strongly type the API, it will automatically generate docs. This also extends to pydanic which we use for the database.