Add swagger description for clan endpoints with Nest decorators

[MikhailDeriabin]

General description

The swagger description of all /clan endpoints should be added using the Nest decorators for that

Things to notice

The description itself can be copied from the swagger.json file.

If there is a need of creating i.e. some custom decorators to speed up the documentation process or adding type safety they should be created.

Tasks

• Add the /clan endpoints swagger description