Improve start release workflow

[rolandkakonyi]

Description

1. We don't utilize a CocoaPods cache, which makes the release process slower than needed
2. One might miss the notification about a new PR without explicitly assigning a reviewer for the release PR
3. There is no easy way to test the release workflow

Changes

1. Added the same cache solution we use for ci.yml workflow
2. Assigning the user triggering the release process explicitly as reviewer on the release PR
3. Added new option for dry_run, to enable testing this workflow

Successful run (with dry_run enabled): https://github.com/bitmovin/bitmovin-player-react-native/actions/runs/6588544853

Runtime went from 6 minutes to 3.5 minutes.

Checklist

• 🗒 CHANGELOG entry - not applicable

[zigavehovec]

Looks good!