Support open-ended ranges in dataset search

[MatthewJA]

Expected behaviour

datacube dataset search 'time > 2021-01-01' should product datasets more recent than 2021-01-01

Actual behaviour

This isn't supported and an error is shown:

time > 2021-01-01
        ^
Expected one of:
  * EQUAL
  * IN

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[omad]

This seems like a nice usability addition.

Eventually people learn to work around it by specifying a really high or really low date as one end of the range, which works, but isn't particularly nice.

The fix implementing this could potentially even work in the same way.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.