Enhancement - Custom file name settings

[NirajChaudhary143]

All Submissions:

• Have you followed the Everest Forms Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Previously, file name are generated randomly. This PR gives user to add custom file name.

How to test the changes in this Pull Request:

1. Creare new form and drag file upload.
2. Go to File upload >> Field Options >> Custom File name
3. Insert custom name.
4. Preview form and and upload file.
5. Check entries whether custom file name is set or not.

Dependency PR

Types of changes:

• Bug fix (non-breaking change which fixes an issue)
• Enhancement (modification of the currently available functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you successfully ran tests with your changes locally?
• Have you updated the documentation accordingly?

Changelog entry

Enhancement - Custom file name settings

[riteelama]

LGTM 👍