Support hardcoded locale for better caching

[martin-tarjanyi]

Is your feature request related to a problem? Please describe.

Currently, the caching mechanism uses the locale as the key. This makes sense in some cases but in lots of cases there is no need to support different locales in the API documentation. If there is no locale-specific logic in the API docs, caching is not very effective.

Describe the solution you'd like

Provide the option to hardcode the locale for the API docs and if it is present, use that for docs generation and caching.

Describe alternatives you've considered

Pre-load all expected locales but it would be error-prone and wasteful.

[martin-tarjanyi]

Possibly the already existing disableI18n config property could be used for this purpose. If it is true, use the default locale always for resolution and caching.

Although, on second thought, it would be nice to define the locale explicitly instead of relying on the the default system locale in such scenario.