feat: implement function "today"

[kbavi]

What problem does this PR solve?

Issue Number: close #462

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

[xdlbdy]

the param path is target path ,it isn't an original path

[codecov]

Codecov Report

Merging #464 (b2ba196) into main (2a78cb5) will decrease coverage by 0.46%.
The diff coverage is 36.02%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #464      +/-   ##
==========================================
- Coverage   57.71%   57.26%   -0.46%     
==========================================
  Files         180      186       +6     
  Lines       14614    15031     +417     
==========================================
+ Hits         8434     8607     +173     
- Misses       5552     5792     +240     
- Partials      628      632       +4     

Impacted Files	Coverage Δ
...ernal/controller/trigger/validation/subscripton.go	69.29% <ø> (+0.85%)	⬆️
internal/gateway/proxy/deadletter.go	0.00% <0.00%> (ø)
internal/gateway/proxy/direct.go	73.33% <0.00%> (-5.24%)	⬇️
internal/primitive/transform/function/util/time.go	62.50% <0.00%> (-8.93%)	⬇️
internal/store/segment/server.go	14.10% <0.00%> (-0.03%)	⬇️
internal/trigger/client/gcloud_functions.go	0.00% <0.00%> (ø)
internal/trigger/client/grpc.go	0.00% <0.00%> (ø)
internal/trigger/client/http.go	0.00% <0.00%> (ø)
internal/trigger/client/interface.go	0.00% <0.00%> (-19.24%)	⬇️
internal/trigger/client/lambda.go	0.00% <0.00%> (ø)
... and 32 more

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[Michaelg22]

@avinashb98 We have left some suggestions for you, please have a look.