feat: added all the gravity types as a Zod enum

[nickytonline]

Description

This PR converts the gravity Zod schema from a string to an enum with all the permitted values for gravity to provide a better experience in editors as well as validation of allowed values for gravity.

~I marked this as a breaking change in case anyone using the cloudinary-util package has a value which is not in the newly introduced Zod enum, as previously it was any string. If that is the case, that gravity option probably never worked for them, but just erring on the safe side for a release.~

I haven't made any documentation updates here as there does not appear to be any docs related to the options including gravity, but if there is a separate repository that requires a documentation update, happy to make changes there as well.

Issue Ticket Number

Fixes #170

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Fix or improve the documentation
• [ ] This change requires a documentation update

Checklist

• [x] I have followed the contributing guidelines of this project as mentioned in CONTRIBUTING.md
• [x] I have created an issue ticket for this PR
• [x] I have checked to ensure there aren't other open Pull Requests for the same update/change?
• [x] I have performed a self-review of my own code
• [x] I have run tests locally to ensure they all pass
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes needed to the documentation

[nickytonline]

I've run the build and tests locally, but just wondering if I need to pnpm link into a project like the getCldOgImageUrl to test, or is the test suite here good enough to confirm the fix?

[colbyfayock]

i think the test suite should be good enough!

as far as the docs, ive been linking to the cloudinary docs for a comprehensive look at the actual values so i think you should be good

[colbyfayock]

this is great, thanks @nickytonline!

[colbyfayock]

@all-contributors please add @nickytonline for code

[allcontributors[bot]]

@colbyfayock

I've put up a pull request to add @nickytonline! :tada: