K8s CAS config should support compression out of the box

[aaronmondal]

When you run a build against the K8s example with the --experimental_remote_cache_compression flag, it complains that the remote store doesn't support compression. This could give off a false impression that NativeLink doesn't support compression.

NativeLink does support compression, but the config we currently use in the examples doesn't. We should change the config to a better default to prevent this confusion.

[allada]

We don't support compression yet:
#260

That flag enables compression on the blob level. We support compression on the network level (gzip) with a config. This is not enabled by default because it slows things down, but better if you have slow network.