Updates the default runner debian image sha to the multi-arch image instead of amd64-only. Also symlinks .containerignore -> .dockerignore since docker refuses to read .containerignore.
With that one can build and push multi-arch, like so:
```
docker buildx create --name tranquil-multiarch --driver docker-container --bootstrap
docker buildx build \
--builder tranquil-multiarch \
--platform linux/amd64,linux/arm64 \
-t atcr.io/tranquil.farm/tranquil-pds:0.6.7 \
--push \
.
docker buildx imagetools create \
-t atcr.io/tranquil.farm/tranquil-pds:latest \
atcr.io/tranquil.farm/tranquil-pds:0.6.7
```
if one were so inclined, that is.
Musl is tier 2 on rust support, and glibc is tier 1.
https://doc.rust-lang.org/nightly/rustc/platform-support.html
Generally, glibc rust is reported to be more performant. Could vary due
to any other reason, but in my testing, builds were up to 50% faster
(for docker cross-compilation amd64->arm64 at least).
- pnpm doesn't implicitly ignore post-install scripts anymore which means trying to build the docker image now fails. i've explicitly allowed them but idk could also ignore them maybe not sure what they actually do lol
- added `confirmModulesPurge: false` but not sure what it actually does as it's not documented? but either way it's also required for the `pnpm build` step to succeed non-interactively it seems idk weird stuff
- removed msmtp/sendmail while i was at it just like https://tangled.org/tranquil.farm/tranquil-pds/commit/f176f55862bc4c41472f8697cc2ca069c24d5e37