Remove Datetime data type

[matthewryanwells]

Description

Removes the DATETIME data type as it is made redundant by the presence of TIMESTAMP.

Updated all functions that returned DATETIME to now return TIMESTAMP and removed it from all other functions, tests, and documentation.

Issues Resolved

#1176

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.30%. Comparing base (ac9b5d8) to head (9764fe2).
Report is 358 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1980      +/-   ##
============================================
- Coverage     97.33%   97.30%   -0.04%     
+ Complexity     4657     4621      -36     
============================================
  Files           408      407       -1     
  Lines         12097    11932     -165     
  Branches        829      826       -3     
============================================
- Hits          11775    11610     -165     
  Misses          315      315              
  Partials          7        7              

Flag	Coverage Δ
sql-engine	97.30% <100.00%> (-0.04%)	⬇️

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[Yury-Fridlyand]

You need to rerun spotless on files you modified and commit the changes from spotless

[MitchellGale]

There are some conflicts to resolve @matthewryanwells

[matthewryanwells]

There are some conflicts to resolve @matthewryanwells

Just resolved the merge conflicts

[LantaoJin]

@penghuo @dai-chen I found this change is not presented in 2.x branch, so it should be a breaking change for 3.0.0.