Feat: Support for User

[mqasimsarfraz]

Support user with evaluation e.g:

user: '{{aks.container_user}}'

Fixes #103

Happy to adopt the implementation if we think we there could be better way.

Testing Done:

→ cat ~/.docker/mcp/catalogs/docker-mcp.yaml  | grep 'user:' -C 3
    volumes:
      - '{{aks.azure_dir}}:/home/mcp/.azure'
      - '{{aks.kubeconfig}}:/home/mcp/.kube/config'
    user: '{{aks.container_user}}'
    prompts: 0
    resources: {}
    config:
--
          access_level:
            type: string
            description: Access level for the MCP server, One of [ readonly, readwrite, admin ]
          container_user:
            type: string
            description: Username or UID of the user to run the MCP server container as. This is useful for ensuring that the server has the correct permissions to access the Azure and kubeconfig files. (e.g. 10000 or azureuser)
          allow_namespaces:

→ cat ~/.docker/mcp/config.yaml 
aks:
  azure_dir: /home/qasim/.azure
  kubeconfig: /home/qasim/.kube/config
  access_level: readonly
  container_user: 1000

- Those servers are enabled: aks
- Listing MCP tools...
  - Running mcp/aks with [run --rm -i --init --security-opt no-new-privileges --cpus 1 --memory 2Gb --pull never -l docker-mcp=true -l docker-mcp-tool-type=mcp -l docker-mcp-name=aks -l docker-mcp-transport=stdio --user 1000 -v /home/qasim/.azure:/home/mcp/.azure -v /home/qasim/.kube/config:/home/mcp/.kube/config] and command [--transport=stdio --access-level=readonly --allow-namespaces= --additional-tools=]

- Listing MCP tools...
  - Running mcp/aks with [run --rm -i --init --security-opt no-new-privileges --cpus 1 --memory 2Gb --pull never -l docker-mcp=true -l docker-mcp-tool-type=mcp -l docker-mcp-name=aks -l docker-mcp-transport=stdio --user 1000 -v /home/qasim/.azure:/home/mcp/.azure -v /home/qasim/.kube/config:/home/mcp/.kube/config] and command [--transport=stdio --access-level=readonly --allow-namespaces= --additional-tools=]
  > aks: (15 tools) (2 prompts)

[slimslenderslacks]

This looks great!

[slimslenderslacks]

@mqasimsarfraz looks great. Thanks for this PR! Can you also tell us a bit about the use case. Are there MCP servers out there that you need to run with a different User?

[mqasimsarfraz]

@mqasimsarfraz looks great. Thanks for this PR! Can you also tell us a bit about the use case. Are there MCP servers out there that you need to run with a different User?

@slimslenderslacks Thanks for the quick review and merge! :) I had included more context in #103 but now I opened docker/mcp-registry#180 to showcase which MCP servers needs it.