fix: expose playwright grafana wait timeout

[mturac]

Summary

• add a grafana-timeout input to the Playwright reusable workflow, defaulting to 90 seconds
• pass the timeout to grafana/plugin-actions/wait-for-grafana
• expose the setting through the top-level CI/CD workflow inputs as playwright-grafana-timeout

Fixes #682

Verification

• go run github.com/rhysd/actionlint/cmd/actionlint@latest
• git diff --check

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ tolzhabayev
❌ mturac
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[sunker]

Thanks for raising this PR @mturac! Looks like there's already a PR open that addressed this problem. cc @xnyo