fix: update validators

[Shehryar21]

Implementation description

Before, not having businessName in auth/register endpoint with donor role ended up creating a user but not donor because businessName is a mandatory field. Change in authAPIValidator fixes that. Also made facebookLink and instagramLink optional.

Steps to test

1. Send post request to auth/register endpoint without businessName and request would not go through.
2. Send put request to donor:id endpoint without facebookLink and instagramLink and request should go through.

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
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• 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