Add model and form to add exhibitors.

[marcoag]

Please note this issue can be taken by multiple participants. It will remain open and accessible to all participants until a successful PR is submitted.

WARNING: This is an issue for the new version v3 of the eventyay backend API, make sure you are working with the dev-v3 branch, and that your PRs target that specific branch.

Add model and form to create and edit exhibitors associated to a certain event.

[VishalMyla]

Please assign this issue to me. I'm Working on it.

[github-actions]

We don't assign issues to external contributors. Please comment that you're working on the issue after checking that no one else is, and then send a pull request for it. Thank You!

[gaurangkudale]

I'm working on this issue

[hpdang]

Please note this issue can be taken by multiple participants. It will remain open and accessible to all participants until a successful PR is submitted.