Consider making Preview Envs Opt-In

[meysholdt]

Is your feature request related to a problem? Please describe

By eliminating unneeded preview envs, we can (either, or a mixture):

• save costs by running a smaller Harvester cluster
• increase developer velocity by running preview envs longer.

Describe the behaviour you'd like

Add a with-preview flag to the Werft job to enable preview envs.
Also, add a convenient checkbox to our PR template:

Additional context

Discussion in Slack.

[gtsiolis]

Yes, please! 💯

This is also aligned with our async remote culture.

Sometimes there's no need to run a preview environment altogether depending on files changes (README.md, etc) and given how we work asynchronously keeping a preview environment alive until the reviewer can come back to it becomes unessasary as they have to trigger another deployment, which only takes a few minutes. ⏱️

This has been brought up in the past a few times, see relevant discussion (internal):

Maybe alternatively, or additionally:

1. Introduce push option to skip CI
2. Allow [ci skip] in commit message to skip CI

[meysholdt]

prerequisite: csweichel/werft#148