Switch repository to monorepo setup

[krystofwoldrich]

Description

Currently, we have 7 different packages, in the repository, which makes managing dependencies complex and incompatible with Dependabot, which opens separate PRs for every single package.

Switching to monorepo setup will make the repository easier to manage.

• One PR for the dep update by dependabot
• One yarn install to download all dependencies
• One command to build all package
• The same for lint

The production package:

• / (@sentry/react-native)

Dev packages:

• /samples/expo
• /samples/react-native
• /test/e2e
• /test/typescript/ts3.8
• /test/perf/TestAppPlain
• /test/perf/TestAppSentry