Documentation: Provide performance guidelines for the client code

[b-fein]

Is your feature request related to a problem?

The PR template requests that the client changes are implemented with good performance. However, the client guidelines do not make any suggestions what to look out for.

Describe the solution you'd like

Provide some common pitfalls for performance issues that developers should look out for and give some suggestions for each how they can be avoided/fixed.

Either the existing guidelines page could be extended https://docs.artemis.cit.tum.de/dev/guidelines/client.html, or a dedicated page could be created.

Describe alternatives you've considered

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Additional context

cc @rabeatwork since you are listed as responsible maintainer for performance.

[rabeatwork]

Two of the most important points are already listed in the documents:

• Never call methods from the HTML template. Automatic change tracking in Angular will affect the performance of the application.
• The Artemis client uses lazy loading to keep the initial size of the package below 2 MB.

We can expand the document in the future with some more pitfalls and on how to avoid/fix them.