Add knowledge graph support

What does this MR do?

Add chart support for the GitLab Knowledge Graph service integration.

When global.appConfig.knowledgeGraph.enabled is set to true, this MR:

• Mounts the shared JWT secret file (.gitlab_knowledge_graph_secret) into webservice pods via projected volumes
• Renders the knowledge_graph section in gitlab.yml with enabled and grpc_endpoint settings

Configuration

global:
  appConfig:
    knowledgeGraph:
      enabled: true
      jwtSecret:
        secret: gitlab-knowledge-graph-jwt-v1
        key: knowledge_graph_jwt_shared_key
      grpcEndpoint: "gkg.orbit-stg.gke.gitlab.net:50054"

Related Rails MRs

• gitlab-org/gitlab!224386 (merged) — JwtAuth module, reads secret from Settings.knowledge_graph.secret_file
• gitlab-org/gitlab!224421 (merged) — GrpcClient, reads endpoint from Settings.knowledge_graph.grpc_endpoint

Related issues

gitlab-org/gitlab#591331 (closed)

Author checklist

For general guidance, please follow our Contributing guide.

Required

For anything in this list which will not be completed, please provide a reason in the MR discussion.

• Merge Request Title and Description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline.
• Documentation created/updated.
• Tests added/updated, and test plan for scenarios not covered by automated tests.
• Equivalent MR/issue for omnibus-gitlab opened.

Reviewers checklist

• MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab.
• Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab chart.