Add %home% support for bazelrc imports

[Gormo]

In CI environments with multiple bazel versions running on the same machine it is sometimes not possible to share ~/.bazelrc files between the versions.

This commit adds support for the %home% prefix when using import or try-import and allows the user to specify any bazelrc file relative to $HOME/.

Example workspace .bazelrc file: try-import %home%/.bazelrc_bazel_7

[michajlo]

While more narrow, I think this is still morally equivalent to https://github.com/bazelbuild/bazel/issues/10904#issuecomment-1726682327 and we should resolve the discussions/concerns there.

Is there some other well-known path you could stage these files? Could the CI system manage the RC files, or the args to specify them? Personally, I'm hesitant to add more, non-hermetic ways for bazelrc loading to look for files.