QueryEditor: Display error even if error field is empty

[idastambuk]

What is this feature?
I noticed that errors aren't displayed in the panel when we pass only errors field from Cloudwatch. We'd have to pass error field as well, even though it's deprecated. This adds the support for only errors but keeps it compatible with error.

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Why do we need this feature?

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Who is this feature for?

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Which issue(s) does this PR fix?:

Fixes #

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.

[torkelo]

Looks good!