Add sanitize function for redirect parameter next

[VladyslavTy]

Change description

Problem: The next parameter used with the /login route is incorrectly decoded, so the redirection happens to the wrong URL. When the next parameter contains a + sign, the application encodes it as a space value. For example: ...?next=courses/course-v1:snowflake-sandbox+ACC-PTF+C/course - at the moment of redirection this route will be encoded as ...?next=courses/course-v1:snowflake-sandbox%20ACC-PTF%20C/course where the %20 is encoded space symbol. So, the user will see the 404 page instead of the course page.

Fix: Add the sanitize function which will check the next parameter:

• If the next parameter looks like the course route - replace the + symbols with the right ASCII code %2B
• If the next parameter is not the course route - keep this parameter as it is

Type of change

• [x] Bug fix (fixes an issue)
• [ ] New feature (adds functionality)

Related issues

Related to ENG-567

Checklists

Development

• [ ] Lint rules pass locally
• [x] Application changes have been tested thoroughly
• [x] Automated tests covering modified code pass

Security

• [ ] Security impact of change has been considered
• [ ] Code follows company security practices and guidelines

Code review

• [x] Pull request has a descriptive title and context useful to a reviewer. Screenshots or screencasts are attached as necessary
• [ ] "Ready for review" label attached and reviewers assigned
• [ ] Changes have been reviewed by at least one other contributor
• [ ] Pull request linked to task tracker where applicable

[github-actions[bot]]

Checking git merge conflicts against https://github.com/openedx/edx-platform.git

Comparing with	open-release/nutmeg.master
Benchmark conflicts with main	299
Current conflicts	301
Summary	Adds 2 new conflicts. How can we do better?

Comparing with	master
Benchmark conflicts with main	329
Current conflicts	331
Summary	Adds 2 new conflicts. How can we do better?