feat: implement function "today"

[AmeerIbrahimm]

What problem does this PR solve?

Issue Number: close #462

Issue Number: close #xxx

Problem Summary

The function is used to get the current date(format: YYYY-MM-DD) in a specific TimeZone. And assign it to the target JSON path.
The Time Zone will be UTC if users don't specify it.

What is changed and how does it work?

• adds a new 'function' called today
  reads the time info from data and return it in YYYY-MM-DD format after converting it to the passed/default
• timezone

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

[CLAassistant]

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1 out of 2 committers have signed the CLA.

✅ AmeerIbrahimm
❌ Ameer Ibrahim

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