feat(isVAT): add Italian regex

[fedeci]

This PR adds support to Italian VAT codes validation using isVAT.

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)

[codecov]

Codecov Report

Merging #1536 (d3cf0a6) into master (9dc4ed3) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #1536   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           99        99           
  Lines         1773      1773           
=========================================
  Hits          1773      1773           

Impacted Files	Coverage Δ
src/lib/isVAT.js	100.00% <ø> (ø)

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[profnandaa]

LGTM, thanks for your contrib! 🎉

[profnandaa]

@fedeci -- just fix the merge conflict and the failing builds and we should be good to go.