fix(aiven_organization_application_user_token): optional fields

[byashimov]

Rewrites aiven_organization_application_user_token resource to SDKv2:

• replaces Number type (up to 512 bit values support) with int type
• this resource do not need null type support, hence the plugin framework makes it just complicated
• there are issues with token handler in the old client, uses generated client instead

[byashimov]

tests

[byashimov]

There is a flaky test with deletion which will be fixed with the client update.

[byashimov]

@rriski rebased on main, fixed changelog conflict