Refactored the API call slightly to return less columns

[jcomack]

Context

• Refactors the API request slightly so we don't request unnecessary data.

Summary

This PR can be summarized in the following changelog entry:

• Refactors request to only get the three required columns: Keyphrase, Volume and Trend.

Relevant technical choices:

Test instructions

This PR can be tested by following these steps:

• Checkout this branch.
• Ensure you have a valid SEMrush token present in your database before testing (see Adds OAuth for communication with SEMrush API. #15607 for more information on how to do this).
• Navigate to a new or existing post
• Fill in a keyphrase and click 'Get related keyphrases'.
• Select the desired country and hit 'Change Country'
• Ensure you get a proper response back and all the data is displayed as it should.

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Documentation

• I have written documentation for this change.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

Fixes #

[enricobattocchi]

CR OK 👍

[enricobattocchi]

Acceptance test OK 👍