allow custom docker image (#25)

Author: promiseofcake

src/examples/global-queue.yml

@@ -11,3 +11,5 @@ usage:
             name: workflow-queue
             context: <context-key>
             only-on-branch: main
+            # Optionally specify a custom Docker image:
+            # docker-image: cimg/node:18.0

src/examples/pipeline-queue.yml

@@ -11,3 +11,5 @@ usage:
             name: pipeline-queue
             context: <context-key>
             only-on-branch: main
+            # Optionally specify a custom Docker image:
+            # docker-image: cimg/node:18.0

src/jobs/global-queue.yml

@@ -2,10 +2,14 @@ description: >
   This job ensures only a single defined global workflow is running at a given point in time.
 
 docker:
-  - image: cimg/base:stable
+  - image: << parameters.docker-image >>
 resource_class: small
 
 parameters:
+  docker-image:
+    type: string
+    default: cimg/base:stable
+    description: "Docker image to use for the executor. Defaults to cimg/base:stable."
   debug:
     type: boolean
     default: false

src/jobs/pipeline-queue.yml

@@ -2,10 +2,14 @@ description: >
   This job prevents a workflow within a given pipeline from running until all previous workflows have completed.
 
 docker:
-  - image: cimg/base:stable
+  - image: << parameters.docker-image >>
 resource_class: small
 
 parameters:
+  docker-image:
+    type: string
+    default: cimg/base:stable
+    description: "Docker image to use for the executor. Defaults to cimg/base:stable."
   debug:
     type: boolean
     default: false