Fix nl phone format

[klaaspieter]

Motivation / Background

This Pull Request has been created because faker generates invalid Dutch phone numbers.

Additional information

Checklist

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• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
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[stefannibrasil]

Could you share a bit more of why these are valid now?

[klaaspieter]

Sure! Previously Dutch phone numbers were using a fallback country code (I don't recall the exact one) which made them invalid. I think technically the only thing to make them valid is to use the correct +31 country code.

My PR also adds cell phone number format because only numbers starting with 06 are valid Dutch cell phone numbers. The 06 prefix is reserved for that purpose.

Thinking about it I think I could update my PR so that 06 numbers are part of the normal format as well because they are valid phone number. I think my change makes it so they will never be generated when asking for a normal phone number. Only when asking for a cell phone number.

[stefannibrasil]

Thanks for providing more context. LGTM 👍🏼