Lectures: Improve the file upload for attachments

[julian-christl]

Checklist

General

• I tested all changes and their related features with all corresponding user types on a test server.
• Language: I followed the guidelines for inclusive, diversity-sensitive, and appreciative language.
• I chose a title conforming to the naming conventions for pull requests.

Server

• I followed the coding and design guidelines.
• I added multiple integration tests (Spring) related to the features (with a high test coverage).
• I added @PreAuthorize and checked the course groups for all new REST Calls (security).
• I implemented the changes with a good performance and prevented too many database calls.
• I documented the Java code using JavaDoc style.

Client

• I added multiple integration tests (Jest) related to the features (with a high test coverage), while following the test guidelines.
• I documented the TypeScript code using JSDoc style.

Motivation and Context

As part of my bachelor's thesis, I'm replacing the file upload occurrences with a more secure way.
The first occurrences are the attachments that I'm addressing in this PR.

Description

• Deprecated the file upload endpoint as we want to replace it
• Moved code from the FileResource to the FileService
• Replaced the simple endpoint to create and update attachment units with similar endpoints that take everything in a multipart upload, including attachment unit, attachment and file
• In the client, I replaced old occurrences where we used multiple calls to the server with the new unified call, extended the blob-util.ts for this
• I added tests for the blob-util.ts
• I removed the legacy code from the blob-utils.ts because all browsers we support (.browserlistrc) support the blob constructor

Steps for Testing

Prerequisites:

• 1 Instructor
• 1 Student

Note: While creating and editing, keep track with your student account if everything works out from the student's point of view (especially the download of the files)

1. Create a lecture
2. Create a file lecture unit
3. Update the file lecture unit with full changes
4. Update the file lecture unit gradually (with and without a new file)
5. Create lecture units of other types and make sure nothing is broken

Review Progress

Code Review

• Review 1
• Review 2

Manual Tests

• Test 1
• Test 2

Test Coverage

Class/File	Branch	Line
AttachmentUnitService.java	70%	98%
FileService.java	85%	87.41%
AttachmentUnitResource.java	85%	98%
FileResource.java	77%	88.46%
attachment-unit-form.component.ts	77.58%	91.11%
attachmentUnit.service.ts	70%	100%
create-attachment-unit.component.ts	76.59%	95.34%
edit-attachment-unit.component.ts	77.77%	95.45%
blob-util.ts	88.88%	100%

[b-fein]

Initial pass over the server code, no in-depth code-review yet.

implemented the change requests

[b-fein]

Code re-approve

[ge65cer]

Thanks for the changes, approved.

[JohannesStoehr]

Refactoring looks good

[stefanwaldhauser]

Reapprove

[bassner]

Approved 👍