Add String functions(lower)

[waahhh]

Motivation

• Support for String functions(lower)

Modifications

• Add JpqlLower, JpqlLowerSerializer, dsl for lower function with tests

Commit Convention Rule

• Please commit your modification based by conventional commit:

Commit type	Description
feat	New Feature
fix	Fix bug
docs	Documentation only changed
ci	Change CI configuration
refactor	Not a bug fix or add feature, just refactoring code
test	Add Test case or fix wrong test case
style	Only change the code style(ex. white-space, formatting)
chore	It refers to minor tasks such as library version upgrade, typo correction, etc.

• If you want to add some more commit type please describe it on the Pull Request

Result

• Please describe the result after this PR is merged.

Closes

• #{issue number} (If this PR resolves an issue.)

[shouwn]

Thank you for your contribution! I think it would be better to rename the parameter to value instead of string.

Since I'm releasing Kotlin JDSL 3.0.0 today, I'd like to include this PR in the 3.0.0 release, so I'll merge and fix it.

Thanks again for your contribution.