feat(featured_trainer): choose how many trainers to feature

[kennethrioja]

Summary of changes

• We can now choose how many trainers we want to feature in the home page

Motivation and context

The value 1 was hardcoded, I wanted more

Screenshots

N/A

Checklist

• I have read and followed the CONTRIBUTING guide.
• I confirm that I have the authority necessary to make this contribution on behalf of its copyright owner and agree to license it to the TeSS codebase under the BSD license.