feat: add timezone support

[xjasonlyu]

No description provided.

[ngjaying]

What is the default timezone value? Local? Need to add that to the default kuiper.yaml explicitly. Also, need to add the doc.

[xjasonlyu]

What is the default timezone value? Local? Need to add that to the default kuiper.yaml explicitly. Also, need to add the doc.

The default timezone is UTC. This will prevent behavior changes due to different system’s timezone settings.

I will open another PR for docs.

[ngjaying]

Then we need to explicitly define that in the conf file. I prefer doc change comes with the PR which is helpful for reviewer to understand the code.

[codecov]

Codecov Report

Patch coverage: 61.36% and project coverage change: -0.02 ⚠️

Comparison is base (732d2a6) 60.62% compared to head (8216697) 60.61%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2064      +/-   ##
==========================================
- Coverage   60.62%   60.61%   -0.02%     
==========================================
  Files         279      279              
  Lines       32187    32267      +80     
==========================================
+ Hits        19513    19556      +43     
- Misses      10764    10792      +28     
- Partials     1910     1919       +9     

Impacted Files	Coverage Δ
internal/topo/planner/projectPlan.go	87.10% <ø> (ø)
internal/topo/planner/projectset_plan.go	100.00% <ø> (ø)
pkg/ast/expr.go	0.00% <0.00%> (ø)
pkg/ast/statement.go	64.29% <ø> (ø)
pkg/ast/token.go	92.68% <ø> (ø)
internal/topo/operator/project_operator.go	83.19% <17.65%> (-11.61%)	⬇️
internal/conf/conf.go	56.31% <25.00%> (-0.57%)	⬇️
internal/xsql/parser.go	73.74% <57.14%> (-0.25%)	⬇️
pkg/cast/time.go	82.33% <66.67%> (-0.85%)	⬇️
internal/topo/operator/projectset_operator.go	83.33% <76.92%> (-0.88%)	⬇️
... and 2 more

... and 4 files with indirect coverage changes

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