chore: initial release please setup

[thomaspoignant]

Description

This PR is the initial setup of release please (https://github.com/googleapis/release-please) to manage release inside the mono repo.

This allow to automate release creation PR for the different systems of this repository.

In this PR we also have the initialisation of 2 go module (core and evaluation) that will be used as dependency inside the main go module.

Checklist

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

[netlify]

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

Name	Link
🔨 Latest commit	26ddc92
🔍 Latest deploy log	https://app.netlify.com/projects/go-feature-flag-doc-preview/deploys/68e960c528490f000805279e

[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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.92%. Comparing base (bac636b) to head (26ddc92).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4028   +/-   ##
=======================================
  Coverage   83.92%   83.92%           
=======================================
  Files         137      137           
  Lines        6813     6813           
=======================================
  Hits         5718     5718           
  Misses        885      885           
  Partials      210      210           

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