Enh: Improve file upload/download/image handling and fill metadata

[martin-rueegg]

See

• Enh: Introduce state and other fields to file table and implement interfaces #6523 (comment)

What kind of change does this PR introduce?

• Feature
• Refactor

Does this PR introduce a breaking change?

• Yes

If yes, please describe the impact and migration path for existing applications:

TBA

The PR fulfills these requirements

• It's submitted to the develop branch, not the master branch if no hotfix
• When resolving a specific issue, it's referenced in the PR's description (e.g. Fix #xxx[,#xxx], where "xxx" is the Github issue number)
• All tests are passing
• New/updated tests are included
• Changelog was modified

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

Depends on and includes

• Fix: invalid argument exceptions #6566
• Enh: file fields: metadata #6594