Update/Extend general documentation on Authentication

[m-mohr]

also include some screenshots for a step-by-step guide...

Would say this is a task for EGI, but not sure who I could assign this to.

[przell]

currently this documentaton is pointing to terrascope: https://docs.openeo.cloud/authentication/#terrascope-registration
Is that correct/up to date?

[m-mohr]

Yes, it seems that this is still required for now. See #21

[m-mohr]

@jdries Clarification is required on when Terrascope registration is required (for SH collections? only for batch jobs? see the unresolved comments in #21 for details).

And once not required anymore, we need to remove the Terrascope registration completely.

[jdries]

I replied in the pull request, everything will also 'work' when the registration is not done:

Correct, even batch jobs will work, but might be slower in case multiple unregistered users are using it.
So it is not a huge problem if users skip this, but if they complain later on, I would need some paragraph to point to. For usage monitoring, this is also better, but that doesn't affect user experience yet.

[m-mohr]

@jdries I've updated the authentication page to reflect what has been said in the PR #21 (Terrascope registration is optional, but may affect prior and performance), see 335fe02. Feel free to change or improve.

I'm leaving it up to VITO to move this to a separate page as proposed by @soxofaan in PR #21.