pdfcpu 0.6.0

[christian-heusel]

• chore: update pdfcpu to version 0.6.0
• chore: bump go in the dockerfile to version 1.21
• fix: skip images that cannot be decoded instead of crashing

Superseeds PR #11 😊

This PR will need some extensive testing, maybe that is something you can help with @Splines?

[Splines]

Thanks @christian-heusel for the PR. Sure, I can help with it, but it will take some time as I've never worked with "go" before.
I've set myself a reminder for this weekend to tackle this review.

[christian-heusel]

This is not so much about the code review but rather about building the resulting application (see i.e. the dockerfile in this repo) and feeding it some PDFs and checking that the output pdfs look good and that there are no errors (for example in the browser console) during the pdf processing.

Once the basic testing is done you could update the version in the MaMpf repo 👍🏻

[Splines]

Note I did not forget about this, but have been been busy last weekend. As we have Christmas vacation soon, I will try to do it during that time ;)