Compile clamav from source

[dirkgomez]

Good to see that this repository seems to be alive again.

I've change the Dockerfile (and the Makefile) quite a bit, have a look here: https://github.com/dirkgomez/bucket-antivirus-function/blob/master/Dockerfile

The rationale: it seems much easier to just compile clamav from a binary. I also updated the whole installation to Python 3.8 and moved the installation to /var/task which is the directory where the lambda runtime expects the action.

Would you consider this? If yes, I would prepare a PR.

[YesemKebede]

Thank you @dirkgomez we will take a look and get back to you soon.