Remove max length from group_name

[pretendWhale]

Motivation and Context

Remove constraint on maximum length of group_name, to resolve issues with long group names (particularly for scanned exams).

Your Changes

Description:
Increase limit on group name to 100 characters, both in the database and the model validations

Type of change (select all that apply):

• Bug fix (non-breaking change which fixes an issue)

Testing

Tested in the web interface with scanned exams, ran and updated the model tests.

Questions and Comments (if applicable)

Two points:

• The database migration is not reversible. We could implement a down method, but I wasn't sure how to handle groups with names > 30 characters.
• This PR does not add a limit to repository name length. This could be added.

Checklist

• I have performed a self-review of my own code.
• I have verified that the pre-commit.ci checks have passed.
• I have verified that the CI tests have passed.
• I have reviewed the test coverage changes reported on Coveralls.

Pull request to make documentation changes (if applicable)

[coveralls]

Pull Request Test Coverage Report for Build 5580058980

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 91.69%

---

Totals
Change from base Build 5548616008:	0.0%
Covered Lines:	37109
Relevant Lines:	39937

---

💛 - Coveralls

[david-yz-liu]

@pretendWhale great research, the "path length" argument we were discussing really applies to repo name, not group name. Given this, let's just drop the group_name length validation altogether.

[david-yz-liu]

@pretendWhale oh please also add a Changelog entry.