Add a `datadog-ci synthetics upload-application` action

[blimmer]

We're currently using this fastlane plugin to upload our DSYMs. It would be nice if there were an action to upload an application version for synthetics tests.

Here are the docs on this.

And here's the help from the NPM package:

datadog-ci synthetics upload-application [--config #0] [--apiKey #0] [--appKey #0] [--datadogSite #0] [--fips] [--fips-ignore-error] [--mobileApp,--mobileApplicationVersionFilePath #0] [--mobileApplicationId #0] [--versionName #0] [--latest]
  Upload a new version to an existing mobile application in Datadog.

[maxep]

Hey @blimmer 👋

Thanks for the suggestion, it makes sense! I have shared it with the Synthetics team 👍