[Playground] Remove example bucket

[MakarkinSAkvelon]

resolves #22367
Playground does not use Example bucket anymore
Terraform code was changed
Readme file was changed

---

Thank you for your contribution! Follow this checklist to help us incorporate your contribution quickly and easily:

• Choose reviewer(s) and mention them in a comment (R: @username).
• Mention the appropriate issue in your description (for example: addresses #123), if applicable. This will automatically add a link to the pull request in the issue. If you would like the issue to automatically close on merging the pull request, comment fixes #<ISSUE NUMBER> instead.
• Update CHANGES.md with noteworthy changes.
• If this contribution is large, please file an Apache Individual Contributor License Agreement.

See the Contributor Guide for more tips on how to make review process smoother.

To check the build health, please visit https://github.com/apache/beam/blob/master/.test-infra/BUILD_STATUS.md

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI.

[olehborysevych]

LGTM (please check RAT)

[rshamunov]

LGTM

[damondouglas]

@pabloem LGTM I was able to provision the infrastructure successfully. However, I was still unable to fully test as the docker images didn't build as a result of ./gradlew playground:terraform:gkebackend -Pproject_environment="environment_name" -Pdocker-tag="tag" -Pdns-name="playground.zone". I will keep watching and testing for future fixes of our docker image build process.