ci: added scorecard report badge

[sarvsav]

Description

The openssf scorecard gives the security health metrics of the project.
More details can be found here.

• This change adds a github action to generate the report.
• updates the README file to show the badge with score.
• updates the index for readme file

Checklist

• I have updated the documentation (README.md and /website/docs)
• I have followed the contributing guide

[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

[netlify]

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

Name	Link
🔨 Latest commit	b0c7fe3
🔍 Latest deploy log	https://app.netlify.com/projects/go-feature-flag-doc-preview/deploys/68c020743530cb000895e77d

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.53%. Comparing base (c867646) to head (b0c7fe3).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3701   +/-   ##
=======================================
  Coverage   83.53%   83.53%           
=======================================
  Files         135      135           
  Lines        6670     6670           
=======================================
  Hits         5572     5572           
- Misses        887      888    +1     
+ Partials      211      210    -1     

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[thomaspoignant]

Hey thanks for this, the score is not super great.
Before merging this I would like to address some of the recommendation first.

[thomaspoignant]

BTW @sarvsav I also working on the recommandation to increase the score.

[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

[thomaspoignant]

I'll merge this one because we have done some improvement.