support Podman for local development

Nobody has claimed this yet.

Some contributors may want to use [Podman](https://docs.podman.io/en/latest/index.html) locally to run containers. The scripts and documentation should be updated to support this use case **in addition to the current use case of using Docker**. From my initial testing, here are some things that need to be addressed:

- use `podman` command instead of `docker` in scripts (e.g. https://github.com/projectcontour/contour/blob/main/test/scripts/make-kind-cluster.sh, `make container` command)
- set `KIND_EXPERIMENTAL_PROVIDER=podman`
- the format of the `podman network inspect` output is different than that of `docker network inspect`, which breaks https://github.com/projectcontour/contour/blob/main/test/scripts/make-kind-cluster.sh#L78-L89 -- update for the podman format
- `kind load docker-image` does not work when using Podman -- need to replace with `podman save image | kind load image-archive -` (ref. https://github.com/projectcontour/contour/blob/main/test/scripts/install-contour-working.sh#L37, https://github.com/kubernetes-sigs/kind/issues/2729#issuecomment-1110152680)

Ultimately, running commands like `make install-contour-release` and `make install-contour-working` should work properly with Podman.

Start with test/scripts/make-kind-cluster.sh, especially the network inspection logic, and test/scripts/install-contour-working.sh, then inspect the make container and install-contour-release/install-contour-working commands. Run the existing local-development workflows with Podman and compare their behavior with Docker. Done means both install commands work with Podman while the current Docker use case remains supported.

Written by the indexing model from the issue text.