Added a warning to Hosted providers page

[eva-vashkevich]

Summary

Fixes #15391

Added a warning that editing cluster will not be possible if provider is disabled

Occurred changes and/or fixed issues

Technical notes summary

Areas or cases that should be tested

Providers -> Hosted providers -> Check that new banner is shown

Areas which could experience regressions

None

Screenshot/Video

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
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[mantis-toboggan-md]

1 tiny thing: that :key property causes console warnings

[mantis-toboggan-md]

LGTM