fix: Use callbacks to set headers for base loader

[wayfarer3130]

Context

The new progressive retrieve doesn't go through the XMLHttpRequest framework, so is missing authentication headers.
This change only updates the default request to go through the old framework unless specifically configured otherwise.

Changes & Results

Testing

Run OHIF linked to this build against an OIDC provider, OR put a breakpoint in a provided beforeSend method to update the header values.

Checklist

PR

• [] My Pull Request title is descriptive, accurate and follows the
  semantic-release format and guidelines.

Code

• [] My code has been well-documented (function documentation, inline comments,
  etc.)

• [] I have run the yarn build:update-api to update the API documentation, and have
  committed the changes to this PR. (Read more here https://www.cornerstonejs.org/docs/contribute/update-api)

Public Documentation Updates

• [] The documentation page has been updated as necessary for any public API
  additions or removals.

Tested Environment

• [] "OS:
• [] "Node version:
• [] "Browser:

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[sedghi]

@wayfarer3130 can you please revert this as well? #916

[igoroctaviano]

LGTM