feat: add new keyword for setting locale

[Dor-bl]

Currently, when one would like to set his locale while reusing the robotframework-faker library, he will either need to Import the library with locale argument or add it to the settings section.
There is no way currently (AFAIK) to have multiple locales in use on the same file.
So maybe we can add a new keyword to support setting locale option.
@emanlove FYI