feat: Test if rule format is valid

[thomaspoignant]

Description

Basic rule query check validation for the linter and to validate the flags.

Closes issue(s)

#2786

Checklist

• I have tested this code
• I have added unit test to cover this code
• I have followed the contributing guide

[netlify]

✅ Deploy Preview for go-feature-flag-doc-preview canceled.

Name	Link
🔨 Latest commit	ba37597
🔍 Latest deploy log	https://app.netlify.com/sites/go-feature-flag-doc-preview/deploys/675c822896e66200089920b2

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 84.77%. Comparing base (8ae0c6d) to head (ba37597).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/flag/rule.go	83.33%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2795      +/-   ##
==========================================
- Coverage   84.78%   84.77%   -0.02%     
==========================================
  Files         111      111              
  Lines        5191     5207      +16     
==========================================
+ Hits         4401     4414      +13     
- Misses        626      628       +2     
- Partials      164      165       +1     

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