Development: Remove no longer required secret push token for Jenkins setups

[b-fein]

Checklist

General

• I tested all changes and their related features with all corresponding user types on a test server.
• This is a small issue that I tested locally and was confirmed by another developer 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

• Important: I implemented the changes with a very good performance and prevented too many (unnecessary) and too complex database calls.
• I strictly followed the principle of data economy for all database calls.
• I strictly followed the server coding and design guidelines.

Changes affecting Programming Exercises

• I tested all changes and their related features with all corresponding user types on a test server configured with Gitlab and Jenkins.

Motivation and Context

Since #6682 the builds are no longer triggered in Jenkins from GitLab directly. Instead, Artemis triggers the build by using the regular API authentication of Jenkins.
The secret token was only used to allow GitLab to trigger builds directly in Jenkins. Since this feature is no longer used it can be removed.
It also does not make sense to keep it since it is not required for LocalVC+Jenkins setups.

Description

Removed references to the no longer needed secret-push-token config option.

As should be clear from the server code changes, the secret token is only used when creating the initial build plan. When triggering builds in the Jenkins, Artemis does not use it.

Steps for Testing

Prerequisites:

• a GitLab+Jenkins or LocalVC+Jenkins setup

1. Create a new programming exercise.
2. When making changes to the template or solution repositories the Jenkins build should run and updated results show up in Artemis.

Testserver States

Note

These badges show the state of the test servers.
Green = Currently available, Red = Currently locked
Click on the badges to get to the test servers.

Review Progress

Code Review

• Code Review 1
• Code Review 2

Manual Tests

• Test 1
• Test 2

Test Coverage

unchanged

Screenshots

n/a

@coderabbitai ignore

[dfuchss]

I'll test the PR asap

[dfuchss]

Changes make sense.

[JohannesWt]

Code 👍

[b-fein]

Note: this is not new, but got lost when removing the secret push token section in #9266.

[magaupp]

Code LGTM