add job database implementation that uses stac

[jdries]

To solve still:

• how to detect authentication settings
• use aggregate api -> won't do, that api is still on dev and not clear if it works
• filtering by status doesn't work yet
• avoid dependency on external stac builder library

[soxofaan]

this is quite a large PR and I didn't go through all of it already, just some initial comments

[soxofaan]

some more notes

[soxofaan]

Using private MultiBackendJobManager._normalize_df from get_by_status looks a bit problematic.

It's also used from initialize_from_df, which is ok at the moment, but subject to change (see #667)

Using it in another context than initialize_from_df, like here, seems to indicate that we have to rethink all this initialization business. Not sure yet what to do instead

[VincentVerelst]

Indeed I was hesitant to use it here first, but I see no other way to return an empty dataframe here that has all columns required by the MultiBackendJobManager

[VincentVerelst]

One way to get the MultiBackendJobManager._normalize_df out of initialize_from_df, might be to do a read, normalize, persist at the start of MultiBackendJobManager.run_jobs?

[soxofaan]

I would leave it as MultiBackendJobManager._normalize_df for now, due to lack of better alternative.
We just have to be sure it's included in changes related to #667.

So in that regard, it's important that this MultiBackendJobManager._normalize_df stuff is properly covered by unit tests, so that we immediately see if we would be breaking something

[soxofaan]

I'm a bit short on time to review this deeply, let alone try running some use cases. It's good that half of the PR is unit tests
The PR also just adds a new class and doesn't touch existing code paths. So maybe we can just merge this as is