chore: checkstyle formater & linter

[jeromevdl]

Issue #, if available: #1290

Description of changes:

• Creation of a checkstyle.xml file (based on google_checks, with custom severities)
• Applied it to the whole project (looooooots of changes)

Checklist

• Meet tenets criteria
• Update tests
• Update docs ==> describe how to use that in CONTRIBUTORS guide (in intelliJ) ==> Docs: Add & improve community documentation #1295
• PR title follows conventional commit semantics

Breaking change checklist

RFC issue #:

• Migration process documented
• Implement warnings (if it can live side by side)

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[msailes]

They look like sensible suggestions and the license header is cool

[codecov-commenter]

Codecov Report

Patch coverage: 69.70% and project coverage change: -0.31% ⚠️

Comparison is base (baa3592) 79.65% compared to head (3578847) 79.35%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1316      +/-   ##
============================================
- Coverage     79.65%   79.35%   -0.31%     
- Complexity      639      641       +2     
============================================
  Files            73       73              
  Lines          2345     2446     +101     
  Branches        253      253              
============================================
+ Hits           1868     1941      +73     
- Misses          397      425      +28     
  Partials         80       80              

Files Changed	Coverage Δ
.../cloudformation/AbstractCustomResourceHandler.java	100.00% <ø> (ø)
...loudformation/CustomResourceResponseException.java	100.00% <ø> (ø)
...mbda/powertools/core/internal/LambdaConstants.java	0.00% <ø> (ø)
...wertools/core/internal/LambdaHandlerProcessor.java	100.00% <ø> (ø)
...lambda/powertools/core/internal/SystemWrapper.java	100.00% <ø> (ø)
...mazon/lambda/powertools/idempotency/Constants.java	0.00% <ø> (ø)
...eptions/IdempotencyAlreadyInProgressException.java	100.00% <ø> (ø)
.../exceptions/IdempotencyConfigurationException.java	100.00% <ø> (ø)
...eptions/IdempotencyInconsistentStateException.java	50.00% <ø> (ø)
...eptions/IdempotencyItemAlreadyExistsException.java	100.00% <ø> (ø)
... and 63 more

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[scottgerring]

Can you add something brief in the maintainers guide to this now, because the big maintainers refactor is going to take a bunch of effort and it would be good to capture this requirement quickly now rather than blocking on that.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
24 Code Smells

No Coverage information
0.0% Duplication

[scottgerring]

LGTM