add search_term to account courses api

fixes: CNVS-10517

This adds the ability to search for a course in an account scope based on
course name, course code, and returning a specific course by relative id
or global id.

Test Plan:
  - Create a few courses
    * Make sure the names and codes are different but similar for a wildcard search
  - Call the api with the search_term parameter as a string
    - Search for a specific course name
    - Search for a specific course code
    - Search for a partial course name
    - Search for a partial course code
    - Search for a course based on the id either global or local to the shard
  - Each should return respective results
  - Test other parameters for this API to make sure this change did not affect them.

Change-Id: I13dbca10ef3a14a0771bdd32fc04ddccdfcb805c
Reviewed-on: https://gerrit.instructure.com/28539
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Nick Cloward <ncloward@instructure.com>