Rework upload symbol script

[armcknight]

Description

We currently require an auth token to be provided, and caution against committing the patch to apply to get the symbol upload script to avoid committing auth tokens to the repo:

• sentry-cocoa/develop-docs/README.md

  Lines 86 to 93 in e1c3819

  	## Upload iOS-Swift's dSYMs with Xcode Run Script
  	The following script applies a patch so Xcode uploads the iOS-Swift's dSYMs to Sentry during Xcode's build phase.
  	Ensure to not commit the patch file after running this script, which then contains your auth token.
  	```sh
  	./scripts/upload-dsyms-with-xcode-build-phase.sh YOUR_AUTH_TOKEN
  	```

• sentry-cocoa/scripts/upload-dsyms-with-xcode-build-phase.sh

  Lines 4 to 7 in e1c3819

  	# Use this script to apply a patch so Xcode uploads the iOS-Swift's dSYMs to
  	# Sentry during Xcode's build phase.
  	# Ensure to not commit the patch file after running this script, which then contains
  	# your auth token.

This can now be done using environment variables, so we should rework the script and leave it in the build phases. See the script I wrote for the SE iOS demo: https://github.com/sentry-demos/ios/blob/master/upload-symbols.sh

Ideally, we create a new build config for debug builds that upload symbols. This way, we don't upload a large volume from the standard debug config. We can also configure it to always upload for release builds.

This way developers can freely upload symbols as needed with minimal changes to the git working index.

[philipphofmann]

@armcknight, do you use the upload-dsyms-with-xcode-build-phase.sh? I created this some time ago because I regularly upload the dSYMs via Xcode. Nowadays, I always check symbolication via TestFlight and have even forgotten that this script exists. @brustolin also never uses it. My point is if none of us use it, we don't need to improve it, and we can even discuss removing it.

[armcknight]

Yep, that's fair too, we could consider removing it. It's been a long time since I needed something symbolicated for testing while debugging.

[philipphofmann]

Excellent. I removed it: #4398.