[INTF25] - Change applicant id from int to string

[mxc-maggiechen]

Notion ticket link

Change Database IDs to UUIDS

Implementation description

Change id attribute in Applicant model and type from int to UUIDV4/string.

Steps to test

1. Run the web app and ensure basic functionalities are not broken
2. Follow the steps to test for this ticket: [INTF25] Build fetch application review page query #77 since it is the only one affected

What should reviewers focus on?

• Check if making type of the Applicant model ID UUID would cause any issues with previous migrations

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

[ruiichen]

LGTM 👍🏻