fix: DiscussionsConfigurations admin error

[Anas12091101]

Description

• Create a course with a Course Run having _25 in it. (for example, "06_25_2024")
• In the django admin, go to http://localhost:18010/admin/discussions/discussionsconfiguration and select the configuration object for the course you created.
• You will get an invalid key error, because the context_key in DiscussionsConfiguration is set to primary key and django pass this context_key to the unquote fn which converts "_25" to "%"

Useful information to include:

• Which edX user roles will this change impact? "Developer" and "Operator".
• Screenshots

  • Before

  • After

Supporting information

https://github.com/mitodl/hq/issues/4705

Testing instructions

• Checkout to this branch and follow the steps in description
• Validate that the DiscussionsConfiguration loads perfectly on admin

Deadline

None