feat: rework monorepo with Turborepo; update example apps and CI pipelines

[artus9033]

Summary

This PR:

• reworks the demo application by re-setting up the RN app, adding 2 additional demo apps: Android & iOS brownfield integration; the old integrated (RN source along with native source):
  
• reworks build scripts & Turbo config in the repo to provide scripts & caching for all packages
• reworks the CI pipeline to account for new apps
• adds CONTRIBUTING.md describing the scripts & an examples.mdx page for docs to list and briefly describe each of the example apps in the demo to enhance DX
• adds caching of Turbo caches on GH Actions (.turbo directories) and Android build & Gradle caches
• adds concurrency rules to the CI workflow to stop tasks for non-top commits in a PR
• pins all GH actions to specific sha commit checksums
• migrates from gradle/wrapper-validation-action to the superceding action: gradle/actions/wrapper-validation

The changes address mainly demo apps and CI used to test building a native application using in-source RN app, which firstly did not produce a standalone packaged RN lib artifact and secondly didn't provide the opportunity for testing the CLI. The new setup adds 3 more apps: RN app, iOS consumer app & Android consumer app. The new CI builds the integrated tester app.

Test plan

CI green + all 3 apps working - tested manually.

[okwasniewski]

Nice! Overall looks really good, left few minor comments

[artus9033]

Hi @hurali97 @thymikee @okwasniewski, the PR is ready for review. The CLI part has been decoupled and will be addressed in a separate PR.

[thymikee]

shipit