Replace dropzone JS dependency with a maintained fork.

[GuySartorelli]

Dropzone hasn't been updated since 2021.
There has been no response from the maintainers about the status of the project.
In dropzone/dropzone#2246 a fork was linked to. It seems to have been well maintained for the last year or so, so seems stable enough to swap to.

Acceptance Criteria

• dropzone JS dependency is swapped for the fork

PRs

• DEP Migrate from abandoned dropzone to a maintained fork #1525