[Backport 2.19-dev] Add EARLIEST/LATEST aggregate functions for PPL (#4100)

[ykmr1224]

backport e2a1132 from #4100

(manual backport due to minor conflicts)

[ykmr1224]

doctest is failing due to regex.rst not found.
It is because #4218 haven't merged. I will rebase after it is merged.

> Task :doctest:doctest FAILED
======================================================================
ERROR: test_docs (unittest.loader._FailedTest.test_docs)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/runner/work/sql/sql/doctest/test_docs.py", line 343, in load_tests
    tests.append(get_test_suite(category_manager, category_name, get_doc_filepaths(docs)))
                 ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/runner/work/sql/sql/doctest/test_docs.py", line 355, in get_test_suite
    return create_cli_suite(filepaths, parser, setup_func)
  File "/Users/runner/work/sql/sql/doctest/test_docs.py", line 327, in create_cli_suite
    return docsuite(
        *filepaths,
        parser=parser,
        setUp=setup_func
    )
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/doctest.py", line 2633, in DocFileSuite
    suite.addTest(DocFileTest(path, **kw))
                  ~~~~~~~~~~~^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/doctest.py", line 2555, in DocFileTest
    doc, path = _load_testfile(path, package, module_relative,
                ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                               encoding or "utf-8")
                               ^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/doctest.py", line 253, in _load_testfile
    file_contents = loader.get_data(filename)
  File "<frozen importlib._bootstrap_external>", line 1217, in get_data
FileNotFoundError: [Errno 2] No such file or directory: '/Users/runner/work/sql/sql/doctest/../docs/user/ppl/cmd/regex.rst'

[ykmr1224]

Rebased.