Implement authentication

[MehulKChaudhari]

Issue Description

The feature-flag service currently lacks authentication, which is essential for ensuring secure access to the service. A design document for implementing authentication has already been created by previous developers link. This issue focuses on continuing the work outlined in that design document to implement the authentication mechanism within the feature-flag service

Expected Behavior

We should have authentication for our feature-flag service

Current Behavior

We don't have authentication in our feature-flag backend service.