Feature/add enum validation for pageable

[Picazsoo]

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Summary by cubic

Adds sort enum validation for Pageable in kotlin-spring (spring-boot) by generating a @ValidSort annotation and applying it to paginated operations whose sort parameter has enum values. This blocks invalid sort columns at request time.

• New Features

  • New option generateSortValidation (requires beanValidations=true and library=spring-boot) to generate ValidSort.kt with @ValidSort and SortValidator in configPackage.
  • Detects pageable operations (x-spring-paginated: true or via autoXSpringPaginated) and injects @ValidSort(allowedValues=[...]) when sort has inline or $ref enum values; skipped for non-paginated ops or when sort lacks an enum.
  • Added kotlin-spring/validSort.mustache, test spec petstore-sort-validation.yaml, generator tests, and a sample at samples/server/petstore/kotlin-springboot-sort-validation; CI updated to compile it.

• Migration

  • Enable with generateSortValidation: "true", beanValidations: "true", and library: spring-boot (optionally autoXSpringPaginated: "true").
  • ValidSort.kt is generated under your configPackage; set this if you need a custom package.
  • Add enum values to your sort query parameter to activate validation.

^{Written for commit 58fe32b. Summary will update on new commits.}