feat(helm): add ServiceAccount support to mcp-stack chart

[ppippi-dev]

Summary

• Add optional ServiceAccount configuration for cloud IAM integration (AWS IRSA, GCP Workload Identity)
• Disabled by default (serviceAccount.create: false) to maintain backward compatibility
• Applied to all Deployments and Jobs in the chart

Changes

File	Description
values.yaml	Add serviceAccount section with create, name, annotations, automountServiceAccountToken
_helpers.tpl	Add mcp-stack.serviceAccountName helper function
serviceaccount.yaml	New ServiceAccount template (created only when create: true)
values.schema.json	Add schema validation for serviceAccount
7 Deployments	Add serviceAccountName reference
3 Jobs	Add serviceAccountName reference

Usage Example

serviceAccount:
  create: true
  name: "my-custom-sa"
  annotations:
    eks.amazonaws.com/role-arn: arn:aws:iam::123456789:role/my-role

Validation

• helm lint passes
• helm template renders correctly with default values
• helm template --set serviceAccount.create=true creates ServiceAccount resource