added welkin quickstart script

[shafi-elastisys]

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What does this PR do / why do we need this PR?

This PR introduces bin/quick-start, a script that fully automates the setup of a local Welkin environment which handles kind cluster creation, configuration, and app installation. It also updates the README.md with a simplified "Quickstart" section.
...

• Fixes [5] Rewrite and script quick start #2767

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• Proper commit message prefix on all commits
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  • The change requires migration steps
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  • The public documentation required an update - [link to change](set-me)
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[Zash]

Really nice work!

[cristiklein]

This is a really good and promising start, but I believe we need a few more iterations before it's ready to fly. 😄

My script stopped with [ck8s] CK8S_PGP_FP is unset. See more detailed comments line-by-line.

[cristiklein]

We are converging, but I still found rough edges. Please see line-by-line comments.

[Zash]

[ck8s] ⚠️  Setup finished, but some status checks failed.
[ck8s] ---------------------------------------------------
[ck8s] Please check the logs above.
[ck8s] You can retry the status check with:
[ck8s]   ./bin/ck8s quickstart status
$ ck8s quickstart status
bin/common.bash: line 7: CK8S_CONFIG_PATH: Missing CK8S_CONFIG_PATH

• Which checks failed? (The .issuers.letsencrypt ones probably, otherwise something lost in the helm output)
• What should I set $CK8S_CONFIG_PATH to? Would be nice to print that even in this case