feat: expose enumsAsTypes and enumsAsConst options

[m0nch1]

Description of Changes

This PR adds support for two additional graphql-codegen options in nuxt-graphql-client:

• enumsAsTypes: Outputs GraphQL enums as union string literal types ('A' | 'B') instead of TypeScript enum.
• enumsAsConst: Appends as const to enum objects to allow usage as readonly values in generated artifacts.

Example output with enumsAsTypes: true:

export type SortOrder = 'asc' | 'desc'; // ✅ instead of `enum SortOrder { ... }`

[m0nch1]

@Diizzayy
I’d greatly appreciate it if you could take a moment to review this when you have some time!