[Playground] Examples CD

[eantyshev]

Examples CD optimization

Main feature comparing to the old workflow is running the examples on production backend. This ensures that examples really work after deployment, and saves resources on building a temporary runner

1. Introduce BEAM_USE_WEBGRPC variable in grpc_client.py. It enables WEBGRPC protocol instead of GRPC, to access public production endpoints.
2. Reusable workflow to optimize GH workflows

addresses #23463
addresses #23464
addresses #23465

See example CD run of this job with necessary amendments (private GCP credentials, push GH triggers)
python passes and go doesn't: known issue #23600

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[olehborysevych]

lgtm

[olehborysevych]

R: @damccorm

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Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control

[damccorm]

LGTM, thanks!