Proposal add support for --force-install=package1,package2 to flatpak-pip-generator

[oefterdal]

Sometimes there are issues with installing some packages because the package maintainer has have bumped the requirements for example setuptools adding --no-deps --no-use-pep517 will ignore this and they will install just fine. I know its a bit hacky, but sometimes its a valid option.

--force-install=package1,package2 results to appending --no-deps --no-use-pep517 to the manifests build-command

"build-commands": [
    "pip3 install --no-deps --no-use-pep517 --verbose --exists-action=i --no-index --find-links=\"file://${PWD}\" --prefix=${FLATPAK_DEST} \"package1\""
],

"build-commands": [
    "pip3 install --no-deps --no-use-pep517 --verbose --exists-action=i --no-index --find-links=\"file://${PWD}\" --prefix=${FLATPAK_DEST} \"package2\""
],

Should also check packages against requirements file.

If there is interest for this, I can start working on it.