Remove or modify instructions for updating docdb

[dougollerenshaw]

The aind-data-access-api/blob/dev/docs/source/ExamplesDocDBRestApi.rst document has a section titled "Updating Metadata" that describes how to modify records in docdb.

Since we want people to do database updates through the https://github.com/AllenNeuralDynamics/aind-data-migration-scripts repo, I think we should remove the content from this section and replace it with a link to that repo. This would help avoid having people go rogue and make direct changes to the database without review.

@jtyoung84, @dbirman and @saskiad: Thoughts on this? I'm happy to self-assign and put in a PR to make the change if you agree.

[dougollerenshaw]

Note that I have a PR in to update/improve the README in the data-migration-scripts repo: https://github.com/AllenNeuralDynamics/aind-data-migration-scripts/pull/545

[dougollerenshaw]

a@helen-m-lin voiced a concern in this PR that we should maintain some instructions for direct upserts to the docdb for users that prefer that. I think that could be resolved by modifying the document here to point to the migration scripts repo and note that using the Migrator class is preferred, but to maintain a minimal example of using upsert.