Generate the "requirements.txt" file with "pip freeze"

**Describe the solution you'd like**
Now that #759 and #784 are merged I think that to improve the reproducibility of the project we should generate the `requirements.txt` file with `pip freeze`.

This file should be periodically updated, maybe in every Pwnagotchi version?

If you agree with this I can open a PR.

Start by reviewing the project's current Python dependency and installation configuration to find how dependencies are currently recorded. Generate requirements.txt with pip freeze and verify that it captures the project's installed dependencies; the issue also calls for deciding how the file should be periodically updated.

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