Allow using Brightcove media without valid API Clients

Currently without API client added under /admin/config/media/brightcove/client, we can't have the video rendered successfully with Brightcove media.

However I believe there are cases that we want the brightcove video be able show without API client.

• View the brightcover video in website only, don't need to integrate with Brightcove
• For trial account, API Authentication is even not available (Feature Not Enabled: The area you are trying to access is not enabled for this user.)

Propose solution:
There is a checkbox “Disable Brightcove API” setting under /admin/config/media/brightcove
I assume we can use it to disable the validation while adding API client.