Make content staging static asset size limit configurable

Description

Content staging currently skips storing the actual data_file for static assets larger than the hardcoded 10 MB limit. The staged file metadata is still preserved, including values such as source_key_str and md5_hash, which allows later recovery/import flows to identify the missing asset.

This default behavior is reasonable for many deployments because staged files may be stored remotely and uploading very large assets can be slow or unnecessary. However, some Open edX installations need to support larger static assets during copy, clipboard, or library sync workflows.

Use Case

Operators should be able to configure the maximum static asset size allowed during content staging without modifying platform code.

For example, a deployment may want to allow assets up to 50 MB instead of the current 10 MB default, while another deployment may prefer to keep the existing behavior.

Proposed Solution

Add a Site Configuration value that controls the static asset staging size limit in bytes:

{
  "CONTENT_STAGING_STATIC_ASSET_SIZE_LIMIT_BYTES": 52428800
}

• https://github.com/openedx/openedx-platform/pull/38670

No files or tests are named. Locate the content staging code that skips storing static assets over 10 MB and the Site Configuration handling, then check how the default limit is represented. Done means the CONTENT_STAGING_STATIC_ASSET_SIZE_LIMIT_BYTES value controls the byte limit while the existing default behavior remains unchanged; review pull request 38670 for related work.