SNT-619: Allow custom OH metadata source

[Bewi]

What problem is this PR solving?

Allow custom OH Metadata file source

Related JIRA tickets

SNT-619

Changes

OpenHexa metadata is now in a different datasets and file name has changed.
To not have to change the code in the future, this PR updates the defaults and allow custom value in OH workspace config for the metadata configuration.

How to test

Open the Admin Panel and set the config to be:

{
  "snt_metadata_dataset": "snt-metadata",
  "snt_configuration_dataset": "snt-configuration"
}

If you don't have a setup for Niger, you'll need to set it up, you can reach me for this.

Go to data layers and create a new one, use the open hexa data layer type.
Go through the steps and verify that it works.

Print screen / video

N/A

Notes

Things that the reviewers should know:

• known bugs that are out of the scope of the PR
• other trade-offs that were made
• does the PR depends on a PR in bluesquare-components?
• should the PR be merged into another PR?

Doc

Tell us where the doc can be found (docs folder, wiki, in the code...).