Allow time columns to be compared with > or <

[samjewell]

The UI options for the "Filter data by values" should include the
'greater than / less than' matchers for fields of type time.

If you configure one of these options on a time field in the
panel json (bypassing the UI) the filter works fine, so this
functionality is already supported.

What is this feature?

[Add a brief description of what the feature or update does.]

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.