Prototype extending CLI command group solution

[pPrecel]

Description

As the output of the Design Kyma CLI flow for basic kyma use case we decided to allow extending the kyma-cli v3 API using yaml configuration hosted by teams in ConfigMaps.

As a first step, we should prototype a mechanism fetching Configmaps from a cluster with expecting labels (required for every Configmap extending cli API).

We can start implementing the first features enabled in such a configuration, like command templates. For now, we can start with one of create, delete, get, status, explain, or patch.

AC

• [x] kyma cli is fetching config maps by label in order to offer commands
• [x] kyma cli offers at least one "template command" command that is sourced from a config map, i.e kyma alpha function explain that explains function CR based on the config map
• [x] STRETCH cli offers exemplary "custom commands" that is sourced from a config map, i.e kyma alpha registry config and/or kyma alpha registry image-import
• [x] introduce error handling for config-map parsing

Proposition how such configmap could look like for now:

apiVersion: v1
kind: ConfigMap
metadata:
  labels:
    kyma-cli/extension: resource
    kyma-cli/extension-version: 0.1
  name: function.serverless.kyma-cli
  namespace: kyma-system
data:
  metadata: |
    name: function # name of new commands group
    description: manage functions # description of new commands group
  resource: |
    singular: function
    plural: functions
    scope: namespaced
    kind: Function
    group: serverless.kyma-project.io
    version: v1alpha2
  templateCommands: |
    create: 
      description: create function
      customFlags:
      - name: runtime
        shorthand: "r"
        path: ".spec.runtime"
        type: string
        description: "function runtime"
        default: "nodejs20"
        required: true
      - name: replicas
        path: ".spec.replicas"
        type: int
        description: "function replicas"
        default: 1
        required: false
      - name: source
         shorthand: "s"
         path: ".spec.source.inline.source"
         type: path
         description: "function source code"
      - name: dependencies
        shorthand: "d"
        path: ".spec.source.inline.dependencies"
        type: path
        description: "function dependencies"
        required: false
    patch:
      description: patch function
      customFlags:
      - name: runtime
        shorthand: "r"
        path: ".spec.runtime"
        type: string
        description: "function runtime"
        default: "nodejs20"
      - name: replicas
        path: ".spec.replicas"
        type: int
        description: "function replicas"
        default: 1
        required: false
      - name: source
         shorthand: "s"
         path: ".spec.source.inline.source"
         type: path
         description: "path to file with functions code"
      - name: dependencies
        shorthand: "d"
        path: ".spec.source.inline.dependencies"
        type: path
        description: "path to file with functions dependencies"
        required: false
    delete:
      description: delete function
    explain:
      description: explain function resource
      info: |-
        this resource allows you to deploy code as a service without taking care of architecture and Kubernetes resources
        ...
    get:
      description: get function/s
      parameters:
       - name: runtime
          path: ".status.runtime"
          type: string
       - name: runtime-image
          displayName: "Runtime Image"
          path: ".status.runtimeImage"
          type: string
       - name: configured
          path: ".status.conditions[0].status"
          type: string
       - name: built
          path: ".status.conditions[1].status"
          type: string
       - name: running
          path: ".status.conditions[2].status"
          type: string
  coreCommands: |
    - name: expose
      coreFuncID: expose-function # enables functionality defined for this resource in the cli under name defined in the `name` field
      description: expose function using ApiRule
    - name: migrate # example only
      coreFuncID: migrate-function
       description: migrate something to something...
    - ...
  customCommands: |
    - name: demo
      description: deploy demo Function subscribed for Events and exposed by ApiRule
      target:
        svcName: serverless-controller
        port: 8080
        endpoint: "/cli/demo"
        token:
          fromSecret:
            name: serverless-controller-cli
            item: token # `.data` field name
        parameters:
        - name: functionName
          flag:
            name: name
            shorthand: "n"
            type: string
            description: "function name"
            required: true
        - name: functionRuntime
          flag:
            name: runtime
            shorthand: "r"
            type: string
            description: "function runtime"
            default: "nodejs20"
        - name: gateway
          flag:
            name: gateway
            shorthand: "g"
            type: string
            description: "istio gateway"
            default: "kyma-system/kyma-gateway"
        - name: eventType
          flag:
            name: event-type
            shorthand: "e"
            type: string
            description: "event type"
            default: "demo-function-type"