Enable results redirect servlet for async TAP queries

[stvoutsin]

Description
PR modifies the Async results functionality, by adding a redirect servlet which serves under /results/*. TAP Async results (jobID/results/result) now link to this servlet (/results/resultID.xml) so that when clients make a (authenticated) request to the results endpoint, they are redirected to the actual file which is stored in a Google CDN location. This should lead the client to strip the auth headers from the request, as otherwise would be a breach of HTTP security best policies.

How was this tested
I've built & deployed a Docker image with this version on idfdev, and tested with the following tools:

• topcat (async queries fail with newest Topcat, but his is due to a bug which will be fixed by the author)
• pyvo async queries with CredentialStore authentication)
• pyvo async queries with AuthSession authentication)

Potential issues
I've only tested this on idfdev, but we have several RSP operators who are storing results in a slightly different way (S3 in openstack for example). Could this break for their environment?

[athornton]

Formal approval. I don't have the Java competence anymore to read this fluently, so I'm going with "sure, looks OK from here."