Get page_size from config or use default

[bryantgray]

Description of change

• A page size of 100 can sometimes be too large for zendesk to handle.
• Page size is now an advanced option, with a default value of 100.
  • can be set to any integer between 1 and 1000 (inclusive)

Manual QA steps

• Verified adjusting page size down will lead to a successful response from Zendesk
• Values outside of 1 - 1000 will cause the default page size (100) to be used

Risks

• Low. Only requests that were previously using page size will use the custom page size, if specified.

Rollback steps

• revert this branch