wip: Implement extract epoch

[mkmik]

Which issue does this PR close?

Closes #2785

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #2786 (bec8956) into master (11ae737) will decrease coverage by 0.03%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2786      +/-   ##
==========================================
- Coverage   85.15%   85.11%   -0.04%     
==========================================
  Files         273      273              
  Lines       48076    48096      +20     
==========================================
  Hits        40938    40938              
- Misses       7138     7158      +20     

Impacted Files	Coverage Δ
...tafusion/physical-expr/src/datetime_expressions.rs	69.39% <0.00%> (-8.52%)	:arrow_down:
datafusion/core/src/physical_plan/metrics/value.rs	86.93% <0.00%> (-0.51%)	:arrow_down:
datafusion/expr/src/logical_plan/plan.rs	73.91% <0.00%> (+0.19%)	:arrow_up:

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[alamb]

This PR is more than 6 month old, so closing it down for now to clean up the PR list. Please reopen if this is a mistake and you plan to work on it more