Use updated Raster API endpoint

[hanbyul-here]

Follow up of NASA-IMPACT/veda-backend#234

[anayeaye]

I created a test stack with the new titiler and a copy of the staging database that I needed for testing the veda-docs and I think it could simplify testing the UI changes, too.
https://test-stac.delta-backend.com/
https://test-raster.delta-backend.com/

[hanbyul-here]

I tested with test endpoint that @anayeaye created, and as far as I can check, the update just works out of the box other than titler parameters for post_process

Changes listed: NASA-IMPACT/veda-backend#234 (comment)
NASA-IMPACT/veda-backend#234 (comment)

[danielfdsilva]

@anayeaye I also did some testing to complement @hanbyul-here's one and everything seems to work. We also avoided using urls directly and are instead using the ones returned by the api responses, so the switch is automatic! :)

[hanbyul-here]

VEDA dashboard is now using the updated backend.