NEW Allow changing parallelUploads config in UploadField

[mikaldl]

Description

Adds option to change amount of parallel uploads

Manual testing steps

• Add setMaxParallelUploads in the chain for UploadFields
• Be sure to allow multiple file uploads

Issues

• #1538

Pull request checklist

• The target branch is correct
• All commits are relevant to the purpose of the PR (e.g. no debug statements, unrelated refactoring, or arbitrary linting)
• The commit messages follow our commit message guidelines
• The PR follows our contribution guidelines
• Code changes follow our coding conventions
• This change is covered with tests (or tests aren't necessary for this change)
• Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
• CI is green

As this is my first time contributing for SilverStripe, please let me know what I could do better for future PRs. :) Thanks!

[emteknetnz]

Is 2 the default number of parallelUploads in dropzone itself?

You'll need to build new dist js files:

• use nvm to install node 18
• globally install the yarn with npm
• in vendor/silverstripe/admin run yarn install
• in vendor/silverstripe/asset-admin run yarn build
• add the dist js files in a squashed commit (so there's a total of one commit for this PR)

[mikaldl]

As mentioned in the issue with the link towards the default settings of Dropzone, the default of dropzone is indeed 2.

Also thanks for the heads-up about the building with the tutorial, that was helpful! Added the new build file.

[emteknetnz]

Tested locally, works well. Thanks for the PR 👍