Fix category dropdown of mentor application to match with endpoint update

[Madhawa97]

Purpose

The purpose of this PR is to fix #63

Goals

The category dropdown of mentor application needs to be updated to comply with the backend endpoint changes introduced with this pull request.

Approach

Update the code to use category.uuid instead of category.id.

Screenshots

Checklist

• [x] This PR doesn't commit any keys, passwords, tokens, usernames, or other secrets.
• [x] I have read and understood the development best practices guidelines ( http://bit.ly/sef-best-practices )
• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation

Related PRs

[PR #83 on scholarx/backend](https://github.com/sef-global/scholarx-backend/pull/83) ## Test environment ## Learning

[Madhawa97]

Also the documentation needs to be updated to have,

{
    "categories": [
        {
            "category": "Data Science",
            "id": "95ba00c0-8173-43c4-9573-6b481b4085e2"
        },
        {
            "category": "Random Category",
            "id": "fe7ca629-4f5e-440a-86cb-d54f8b98ec5f"
        },
        {
            "category": "Computer Science",
            "id": "fef68adb-e710-4d9e-8772-dc4905885088"
        }
    ],
    "message": "All Categories found"
}