feat: allow passing pod_install_directory during ios_build job (react-native-community#136)

Author: devnev

src/jobs/ios_build.yml

@@ -20,6 +20,10 @@ parameters:
     description: If we should start the Metro packager in the background for this job.
     type: boolean
     default: false
+  pod_install_directory:
+    type: string
+    default: ""
+    description: The location of the "ios" directory for `pod install`. Will skip `pod install` if missing.
   yarn_cache:
     description: Should we cache after yarn install? Defaults to true
     type: boolean
@@ -101,6 +105,11 @@ steps:
       condition: <<parameters.start_metro>>
       steps:
         - metro_start
+  - when:
+      condition: <<parameters.pod_install_directory>>
+      steps:
+        - pod_install:
+            pod_install_directory: <<parameters.pod_install_directory>>
   - ios_build:
       project_path: <<parameters.project_path>>
       derived_data_path: <<parameters.derived_data_path>>