feat: add `rate()` udf

[discord9]

Add a rate() udf that calc rate of a Monotonic increase counter over its time. Does NOT support reset yet

[codecov[bot]]

Codecov Report

Merging #508 (e031355) into develop (8232015) will decrease coverage by 0.00%. The diff coverage is 92.75%.

@@             Coverage Diff             @@
##           develop     #508      +/-   ##
===========================================
- Coverage    85.71%   85.71%   -0.01%     
===========================================
  Files          412      413       +1     
  Lines        52660    52727      +67     
===========================================
+ Hits         45138    45195      +57     
- Misses        7522     7532      +10     

Flag	Coverage Δ
rust	85.71% <92.75%> (-0.01%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/common/query/src/error.rs	89.52% <33.33%> (-0.87%)	:arrow_down:
src/common/function/src/scalars/math/rate.rs	95.38% <95.38%> (ø)
src/common/function/src/scalars/math/mod.rs	100.00% <100.00%> (ø)
src/sql/src/parser.rs	76.70% <0.00%> (-2.54%)	:arrow_down:
src/servers/src/opentsdb.rs	98.41% <0.00%> (+1.58%)	:arrow_up:
src/servers/src/error.rs	42.10% <0.00%> (+7.89%)	:arrow_up:

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[killme2008]

@discord9 Can you fix the conflicting files?