Partially implement javascript source map upload command

[andrewbrook]

Description

This is a new, partially implemented command for uploading javascript mapping files. The command takes the user-supplied mapping file path, or a path to a directory, and uploads all available *.js.map files to the customer's Google Cloud Storage bucket. If the bucket does not exist yet, it is created.

The next steps for this command are to:

• extract the app version information
• notify Firebase Telemetry of the newly uploaded files

Scenarios Tested

• Uploading a single mapping file
• Specifying and uploading a nested directory of mapping files
• Creating a new GCS bucket
• Changing the location of the GCS bucket

Sample Commands

firebase crashlytics:sourcemap:upload path/to/build/mapping.js.map --app
firebase crashlytics:sourcemap:upload .next --app