Change xr_interpolate extent Error to Warning

[robbibt]

Proposed changes

Previously the xr_interpolate function returned an error if all points were outside the dataset extent. This was an invalid requirement: it's often useful to interpolate from points outside the boundary of a dataset.

This PR changes the error to a warning.

Closes issues (optional)

• Closes Issue #000

Checklist

(Replace [ ] with [x] to check off)

• Notebook created using the DEA-notebooks template
• Remove any unused Python packages from Load packages
• Remove any unused/empty code cells
• Remove any guidance cells (e.g. General advice)
• Ensure that all code cells follow the PEP8 standard for code. The jupyterlab_code_formatter tool can be used to format code cells to a consistent style: select each code cell, then click Edit and then one of the Apply X Formatter options (YAPF or Black are recommended).
• Include relevant tags in the final notebook cell (refer to the DEA Tags Index, and re-use tags if possible)
• Clear all outputs, run notebook from start to finish, and save the notebook in the state where all cells have been sequentially evaluated
• Test notebook on both the NCI and DEA Sandbox (flag if not working as part of PR and ask for help to solve if needed)
• If applicable, update the Notebook currently compatible with the NCI|DEA Sandbox environment only line below the notebook title to reflect the environments the notebook is compatible with
• Check for any spelling mistakes using the DEA Sandbox's built-in spellchecker (double click on markdown cells then right-click on pink highlighted words). For example:

[vnewey]

looks good!