feature: full-spectrum runtime Docker configuration (via #4965)

* reorganize docker things

* Configurator WIP

* implement Docker runtime config generator

* add tests

* update documentation

* fix Markdown tables

* Move Docker section

* add note to README

* move up `nodejs` install for more aggressive caching

* drop exclusive test

* fix missing `DISPLAY_OPERATION_ID`

docker/configurator/translator.js

@@ -0,0 +1,93 @@
+// Converts an object of environment variables into a Swagger UI config object
+const configSchema = require("./variables")
+
+const baseConfig = {
+  url: {
+    value: "https://petstore.swagger.io/v2/swagger.json",
+    schema: {
+      type: "string"
+    }
+  },
+  dom_id: {
+    value: "#swagger-ui",
+    schema: {
+      type: "string"
+    }
+  },
+  deepLinking: {
+    value: "true",
+    schema: {
+      type: "boolean"
+    }
+  },
+  presets: {
+    value: `[\n  SwaggerUIBundle.presets.apis,\n  SwaggerUIStandalonePreset\n]`,
+    schema: {
+      type: "array"
+    }
+  },
+  plugins: {
+    value: `[\n  SwaggerUIBundle.plugins.DownloadUrl\n]`,
+    schema: {
+      type: "array"
+    }
+  },
+  layout: {
+    value: "StandaloneLayout",
+    schema: {
+      type: "string"
+    }
+  }
+}
+
+function objectToKeyValueString(env, { injectBaseConfig = false, schema = configSchema } = {}) {
+  let valueStorage = injectBaseConfig ? Object.assign({}, baseConfig) : {}
+  const keys = Object.keys(env)
+
+  // Compute an intermediate representation that holds candidate values and schemas.
+  // 
+  // This is useful for deduping between multiple env keys that set the same
+  // config variable.
+
+  keys.forEach(key => {
+    const varSchema = schema[key]
+    const value = env[key]
+    
+    if(!varSchema) return
+
+    const storageContents = valueStorage[varSchema.name]
+
+    if(storageContents) {
+      if(varSchema.legacy === true) {
+        // If we're looking at a legacy var, it should lose out to any already-set value
+        return
+      }
+      delete valueStorage[varSchema.name]
+    }
+
+    valueStorage[varSchema.name] = {
+      value,
+      schema: varSchema
+    }
+  })
+
+  // Compute a key:value string based on valueStorage's contents.
+
+  let result = ""
+
+  Object.keys(valueStorage).forEach(key => {
+    const value = valueStorage[key]
+    
+    const escapedName = /[^a-zA-Z0-9]/.test(key) ? `"${key}"` : key 
+
+    if (value.schema.type === "string") {
+      result += `${escapedName}: "${value.value}",\n`
+    } else {
+      result += `${escapedName}: ${value.value === "" ? `undefined` : value.value},\n`
+    }
+  })
+
+  return result.trim()
+}
+
+module.exports = objectToKeyValueString