Updated source_mat_id on submission portal

[mslarae13]

I've updated the description & guidance for source_mat_id.

See: https://docs.google.com/spreadsheets/d/1cMlPKgjZh-v21aMYCm9x1TxzE5BwGQptBQcvuaYAtC8/edit#gid=1241218612
Row 77, 78, 79

In accordance with microbiomedata/nmdc-schema#372 feedback.

Updates need added to data harmonizer and the submission portal.

[mslarae13]

Adding to SubPort squad. I think this is done? Need to confirm.

[turbomam]

This issue mentions the following issue with closed status:

• Improve description for globally unique ID nmdc-schema#372

But neither this issue or the linked issue mention a PR. If there was a merged PR, that's usually strong grounds to close all linked issues. But we'll have do some manual double checking in this case.

[mslarae13]

Did a quick check! Looks like I edited the linked google sheet https://docs.google.com/spreadsheets/d/1cMlPKgjZh-v21aMYCm9x1TxzE5BwGQptBQcvuaYAtC8/edit?usp=sharing

But made no changes to the schema. I can go ahead and make a branch for this and update it in the schema.

[mslarae13]

microbiomedata/nmdc-schema#683