[Playground] support for Kafka-enabled examples (#24459)

* [Playground][Backend]updated python scripts to process datasets

* [Playground] [Backend] updated tests for a helper

* [Playground] [Backend] resolved comments after review

* [Playground] [Backend] minor fixes

* [Playground] [Backend] removed a transaction for a datastore client

* [Playground] [Backend] updated endpoints to get precompiled objects

* [Playground] [Backend] updated tests for a pc mapper

* [Playground] [Backend] edited a response

* [Playground] [Backend] edited datasets field as an embeded entity

* [Playground] [Backend] edited pc response with datasets

* [Playground] [Backend] changed variable names

* [Playground] [Backend] updated requirements txt file

* [Playground] [Backend] updated python scripts after review

* -ast

* [Playground] [Backend] updated python scripts after a second review

* [Playground] [Backend] added additional validation

* [Playground] [Backend] added dataset bucket name variable to github workflows

* [Playground] [Backend] removed cloud storage client

* [Playground] [Backend] removed unused env variable

* [Playground] [Backend] renamed link field to path

* [Playground] [Backend] updated the method to run code to process examples with an emulator

* [Playground] [Backend] updated python scripts to handle examples with emulators

* [Playground] [Backend] updated unit tests

* [Playground] [Backend] refactoring

* [Playground] [Backend] updated contribute md file

* [Playground] [Backend] removed cloud storage

* [Playground] [Backend] fixed test data generation

* Fixes after merge

* FIx for Java docker container

* fix

* fixes

* rat

* debug show logs

* debug

* optimize router Dockerfile

* fixed image

* checker self-check

* -storage client

* go.mod

* snippet

* generateProto

* -licenses

* adjust checker

* java Dockerfile

* infrastructure/GCS -> local

* examples

* nit

* nit

* controller_test

* Java classes renamed

* Resolved compilation warnings for java Kafka examples

* nit

* nit

* recover

* DEBUG

* Revert "DEBUG"

This reverts commit 87c62f0e93a185a44d0e605af6183ecdf5639bda.

* revert

* revert

* revert

* spotless

* datastore_transaction

* nits

* example

* Examples amended

* spotless

Co-authored-by: Vladislav Chunikhin <vladislav.chunikhin@akvelon.com>
Co-authored-by: Ruslan Shamyunov <ruslan.shamunov@akvelon.com>