feat: [Validation] add field_exists rule

[kenjis]

Needs #8131

Description
For #8006

• add rule to check if the field exist in the data

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

Ah, we need to handle the key with dot array syntax?

[MGatner]

Good call, I'm afraid so. See required_without above. May be worth having a private method for $data transformations.

[MGatner]

Ah, I see your next PR - much better solution.

[kenjis]

Yes, done.

[michalsn]

I believe we would also need versions _with and _without.

Yes for dot array syntax. I see it's already done.

[kenjis]

I believe we would also need versions _with and _without.

Really?
Do you have a use case?

[michalsn]

Sorry, I forgot about this one.

Example... an API with a custom payload? Some optional fields depend on selected parameters. They're not required though.

I think I saw a request like this a long time ago, but I can't find it now.

[kenjis]

I think we can use required_with in most cases.

Some optional fields depend on selected parameters. They're not required though.

If it is not required, then it is okay that the key does not exists in the data.
Also, if it depends on selected parameters, we need to write custom rule?

If it is required, and the value may be null, empty string, then we need field_exists_with.

[MGatner]

Looks good to me. I think starting here makes sense and if we find need for additional related rules they can follow.