Allow multiple parameters for gzip_proxied

[promarcel]

In commit 536e613 (PR #1520) a custom type for the gzip_proxied parameter has been added, which is great to add further validation for inputs.

But due to the official NGINX documentation the parameter gzip_proxied allows multiple parameters (https://nginx.org/en/docs/http/ngx_http_gzip_module.html#gzip_proxied), which is not covered by the current type:

type Nginx::GzipProxied = Enum['off', 'expired', 'no-cache', 'no-store', 'private', 'no_last_modified', 'no_etag', 'auth', 'any']

In detail there is not working an array of options (['expired', 'no-cache', 'no-store', 'private', 'auth']) or a string with multiple parameters ('expired no-cache no-store private auth').

This should not be the expected behavior if the official documentation allows multiple parameters. As a current workaround http_cfg_append can be used to allow configuration of multiple parameters.