[PP-1] Alt and Title options and requiredness should be honored in Internal HTTP Media API

Overview

In #3578449: Add an unstable (v0) "canvas_external_api" POST route for uploading an image blob and getting back the ID and UUID of the created media entity we added a internal HTTP API for managing media library images.
But it took alt and title as optional for the image.
However, the image field in the media entity can have "Enable (Alt|Title)" and "(Alt|Title) field required" checked or unchecked.

We should honor those settings.

Proposed resolution

Validate the request based on "Enable (Alt|Title)" and "(Alt|Title) field required" values on the field config.

User interface changes

None.