ref(samples): improve samples & SPM docs

[buenaflor]

Improves upon the samples and added the sample from #71. Ref: #81

All Android samples are now automatically configured to run in release mode and will automatically upload proguard mapping files.
All iOS samples will automatically upload dsym files.

I've also adjusted the sample from #71 to use SPM and added some docs on how to use SPM instead of Cocoapods.

The run configuration for these samples should also automatically be setup through Android Studio

[buenaflor]

@marandaneto sry there's a lot of file changed, that's because I had to rearrange and rename the examples.

Most significant changes:

• README -> adds SPM docs
• Sample README -> add doc on how to start the samples
• samples/scripts -> added two shell scripts that prepare the app builds
• Sentry agp -> added the Sentry AGP to every Android build.gradle.kts for proguard upload
• Add another sample using SPM (copy pasted the one using cocoapods)

If you have time could you check if the samples work for you now

[marandaneto]

@buenaflor
CI is unhappy.

error: An organization slug is required (provide with --org)

Task :sentry-samples:kmp-app-cocoapods:androidApp:uploadSentryProguardMappingsRelease FAILED

compressing mappings
Add --log-level=[info|debug] or export SENTRY_LOG_LEVEL=[info|debug] to see more output.
uploading mappings
Please attach the full debug log to all bug reports.

[buenaflor]

@marandaneto yep, I know where the issue is, I'll get to it

[buenaflor]

@marandaneto it's finally green ✅

[marandaneto]

Nice @buenaflor