Add metadata contributor roles to submission portal diataxis documentation

[mslarae13]

Below are the contributor roles. We should update the documentation here: https://nmdc-documentation.readthedocs.io/en/latest/howto_guides/submit2nmdc.html

to include this information. At least, I think it's this? @jkelliher-github curious on your thoughts about where we should include this information

Relates to https://github.com/microbiomedata/nmdc-server/issues/1162

• Editor: Editors of a submission have full permission to edit every aspect of the submission with the exception of permission levels.
• Owner (Author?): Submission author and Principal Investigator have full permission to edit every aspect of the submission.
• Viewer: A viewer can see all components of a submission, but cannot edit.
• Metadata Contributor: A metadata contributor can view all components of a submission and can only edit the sample metadata information on the last step of the submission process.

Criteria for completion

• [ ] Information about contributor roles is available in the documentation.

[mslarae13]

FYI @eecavanna for documentation squad