feat: support greatest function

[NiwakaDev]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

This PR adds support greatest(Date, Date) like this:

select GREATEST('1999-01-30', '2023-03-01');

Will generate:

+-------------------------------------------------+
| greatest(Utf8("1999-01-30"),Utf8("2023-03-01")) |
+-------------------------------------------------+
| 2023-03-01                                      |
+-------------------------------------------------+

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

Related to #1536.

Resources

This PR is based on:

• date functions
• date type

[codecov]

Codecov Report

Merging #2490 (fd6f82d) into develop (40781ec) will increase coverage by 0.06%.
Report is 35 commits behind head on develop.
The diff coverage is 77.51%.

❗ Current head fd6f82d differs from pull request most recent head 4e2539a. Consider uploading reports for the commit 4e2539a to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2490      +/-   ##
===========================================
+ Coverage    84.83%   84.90%   +0.06%     
===========================================
  Files          726      730       +4     
  Lines       115028   116085    +1057     
===========================================
+ Hits         97586    98558     +972     
- Misses       17442    17527      +85     

[killme2008]

Almost LGTM, a little suggestion. Thank u very much.

[killme2008]

@waynexia PTAL

[waynexia]

rest LGTM

[killme2008]

@NiwakaDev Thank you for your contribution and patience.