Feature/#203 ci remove entry point at merge

Feature

Summary

This MR provides an automatic removal of the entry point in src/index.template.html if present.

It also removes an unused stage from the CI config.

❗ This feature has only been tested locally. To test if it's fully functioning in the repository, we have to merge it an then merge another MR with an entry point set.

Does the result of the MR comply to our "definition of done"?

• Unit tests passed
• Code reviewed
• Acceptance criteria met
• Functional tests passed
• Non-Functional requirements met
• Product Owner accepts the User Story

Tests

Are we able to test this new feature?

• No, it is not possible (cf. MR description)

Closes

Closes #203 (closed).

/cc Mathias Göbel, Frank Schneider, Michelle Weidling