DG-1907 Validate Channel Link

[nikhilbonte21]

Change description

We currently have frontend-only validation for the correct Slack link at the Persona “Add Link” CTA. However, the endpoint can insert a malicious link into the product.

We would want to have the same validation from the backend as well. Please check the linked security ticket for details.

Regex details - https://atlanhq.atlassian.net/browse/DG-1907?focusedCommentId=270252
Testing - https://atlanhq.atlassian.net/l/cp/Qm0GkvQR

Type of change

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

Related issues

https://atlanhq.atlassian.net/browse/DG-1907

Checklists

Development

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

Security

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

Code review

• 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

[hr2904]

Testcases LGTM, Code changes LGTM.