Devcontainer no longer builds after recent base image change

[tsaarni]

The Devcontainer fails to build and start after recent changes.

It seems likely that this regression is related to #39679 which (due to other recent DRY refactoring #42060), switched also the devcontainer base image from Ubuntu to Debian.

I’m observing the following issues:

• apt install failure: libpython2.7 package is no longer available. fixed by devcontainer: fix dev container #42405
• Cannot assign the group for the user: the pcap group does not exist.
• Mapping the container user to the host uid/gid no longer works, causing the workspace to be non-writable.
• clangd does not find std library headers anymore.

[phlax]

yeah - apologies for breakage here - in the case of the #42060 i did at least have a vscode-using colleague test this - but i didnt remember to do so when switching the toolchains

it is indeed now debian and much smaller - i set it iirc to use the devtools variant - which has some additional utils etc to what ci uses - happy to fix upstream if there are issues wrt user mappings (repo is https://github.com/envoyproxy/envoy-build-tools/)

[tsaarni]

This issue was partly addressed by #42405.
Hopefully rest will be fixed in #42415.