Gym search member count

[tvaroglu]

• Changes Implemented:

  • Add new attribute to GymSerializer to return gym_member_count (for the Gym Search page #86)
  • Update GymService to return 50 instead of 20 gyms

• Quality Control Checklist:

  • [x] Code adheres to Rubocop styling (if unavoidable infractions, please clarify below)
  • [x] 100% SimpleCov test coverage (if below, please clarify below)
  • [x] Last Commit passes CircleCI build

• Blockers (if applicable):

• Next Steps & Additional Notes:

  • Need FE to update Gym PORO to accept new attribute.
  • Placeholders are already pre-built within views and associated spec files, should be a quick hitter

[tvaroglu]

Sweet good work! I will go to the front end tomorrow and change the poro to use this new call in the views!

Thank you in advance! Please keep me posted on progress, as I assume we'll want to merge in this PR along with (right before) the FE one to keep Circle happy. Can pull this out of draft as soon as it's needed.