Update conan api documentation for new v2 endpoint

Update the conan api documentation: https://docs.gitlab.com/api/packages/conan/ for the new conan v2 api endpoint that have already been merged.

references

List of MR that missed documentation:

• !176600 (merged)
• !181393 (merged)
• !182379 (merged)
• !177259 (merged)
• !177226 (merged)

$ r grape:routes | grep "conan" | grep "v2"

GET /api/:version/projects/:id/packages/conan/v2/users/check_credentials(.:format) - Check for valid user credentials per conan CLI
GET /api/:version/projects/:id/packages/conan/v2/conans/search(.:format) - Search for packages
GET /api/:version/projects/:id/packages/conan/v2/conans/:package_name/:package_version/:package_username/:package_channel/latest(.:format) - Get the latest revision
GET /api/:version/projects/:id/packages/conan/v2/conans/:package_name/:package_version/:package_username/:package_channel/revisions/:recipe_revision/files/:file_name(.:format) - Download recipe files
PUT /api/:version/projects/:id/packages/conan/v2/conans/:package_name/:package_version/:package_username/:package_channel/revisions/:recipe_revision/files/:file_name(.:format) - Upload recipe package files
PUT /api/:version/projects/:id/packages/conan/v2/conans/:package_name/:package_version/:package_username/:package_channel/revisions/:recipe_revision/files/:file_name/authorize(.:format) - Workhorse authorize the conan recipe file