feat: Validation for dominica [en-DM] phone number added

[RafyBrens]

• Created a regular expression to validate Dominica phone numbers.
• The regex supports both international and local formats, ensuring compatibility with various phone number representations.
• Added test cases to verify the correctness of the new regex pattern.

https://en.wikipedia.org/wiki/Area_code_767 https://www.itu.int/itudoc/itu-t/number/d/dma/81906_ww2.doc

Checklist

-Issue 2506

• [x] PR contains only changes related; no stray files, etc.
• [x] README updated (where applicable)
• [x] Tests written (where applicable)
• [x] References provided in PR (where applicable)