chore: add spotless format checker

[hezean]

• checks format in build ci
• auto add license header

[codecov-commenter]

Codecov Report

Merging #28 (444cbdc) into main (1995d50) will decrease coverage by 0.04%.
The diff coverage is 98.30%.

@@             Coverage Diff              @@
##               main      #28      +/-   ##
============================================
- Coverage     76.74%   76.70%   -0.05%     
- Complexity      268      274       +6     
============================================
  Files            31       31              
  Lines           972      970       -2     
  Branches         68       68              
============================================
- Hits            746      744       -2     
  Misses          184      184              
  Partials         42       42              

Impacted Files	Coverage Δ
.../java/com/featureprobe/sdk/server/AccessEvent.java	100.00% <ø> (ø)
...va/com/featureprobe/sdk/server/AccessRecorder.java	97.67% <ø> (ø)
...featureprobe/sdk/server/DefaultEventProcessor.java	71.87% <ø> (ø)
...probe/sdk/server/DefaultEventProcessorFactory.java	100.00% <ø> (ø)
.../com/featureprobe/sdk/server/EvaluationResult.java	72.72% <ø> (ø)
...c/main/java/com/featureprobe/sdk/server/Event.java	66.66% <ø> (ø)
...in/java/com/featureprobe/sdk/server/FPContext.java	67.39% <ø> (ø)
...ain/java/com/featureprobe/sdk/server/FPDetail.java	80.00% <ø> (ø)
...java/com/featureprobe/sdk/server/FeatureProbe.java	64.46% <ø> (ø)
.../com/featureprobe/sdk/server/FileSynchronizer.java	65.00% <ø> (ø)
... and 21 more

[hezean]

awaiting for #29 to be merged

[gangb-tech]

This pull request has been merged into #35