add COURSE_SEARCH_API_URL and CONTENT_FILE_SEARCH_API_URL

[gumaerc]

Description/Context

In order to support the work being done in mitodl/ocw-hugo-themes#1313, two new settings / environment variables need to be added: COURSE_SEARCH_API_URL and CONTENT_FILE_SEARCH_API_URL. These values need to be set in ThemeAssetsPipelineDefinition so that the new search API URL's are baked into the Javascript bundles generated for the site.

Plan/Design

• Add COURSE_SEARCH_API_URL as a Django setting pulled from the environment with a sane default
• Add CONTENT_FILE_SEARCH_API_URL as a Django setting pulled from the environment with a sane default
• In ThemeAssetsPipelineDefinition, inject the values of these settings into the params section of build-ocw-hugo-themes-task