test(tvix/[ca]store): enable bigtable only with "integration" feature

The emulator and bigtable client are quite big. Remove them from the
default //tvix:shell.

Put the tests behind a `integration` feature flag, and add a variant
with that enabled to CI, and drop the bigtable tools from //tvix:shell.

Change-Id: Ie042097a0d6fc26542faa96c139b77298ccb160a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11582
Reviewed-by: edef <edef@edef.eu>
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/store/src/pathinfoservice/from_addr.rs

@@ -208,7 +208,7 @@ mod tests {
     #[case::grpc_invalid_host_and_path("grpc+http://localhost/some-path", false)]
     /// A valid example for Bigtable.
     #[cfg_attr(
-        feature = "cloud",
+        all(feature = "cloud", feature = "integration"),
         case::bigtable_valid(
             "bigtable://instance-1?project_id=project-1&table_name=table-1&family_name=cf1",
             true
@@ -216,7 +216,7 @@ mod tests {
     )]
     /// An invalid example for Bigtable, missing fields
     #[cfg_attr(
-        feature = "cloud",
+        all(feature = "cloud", feature = "integration"),
         case::bigtable_invalid_missing_fields("bigtable://instance-1", false)
     )]
     #[tokio::test]