Add Estonia country_code

[HassanAkbar]

Fixes #3098
This Pull Request adds country_code to Estonia.
For Germany, its working as expected e.g,

Faker::Config.locale = :de
pp Faker::PhoneNumber.phone_number_with_country_code  # +49 245-1176794

It returns +49 which is an expected behavior.

Additional information

Checklist

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[thdaraujo]

thank you!

[thdaraujo]

[Correctable] Lint/AmbiguousRegexpLiteral: Ambiguous regexp literal. Parenthesize the method arguments if it's surely a regexp literal, or add a whitespace to the right of the / if it should be a division.
    assert_match /\+372\s?\d{3}\s?\d{4}/, phone_number

[HassanAkbar]

@thdaraujo Thanks for review. Fixed 👍