feat(tvix): add //tvix:shell-integration

This provides a shell containing the necessary packages to run the
integration tests too.

//tvix:shell stays the same.

Change-Id: Iac7977cbb7dc085da698993be9baca662d09ff5f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/13164
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: Connor Brewster <cbrewster@hey.com>

tvix/shell.nix

@@ -25,6 +25,7 @@
       })
     ];
   })
+, withIntegration ? false
 , ...
 }:
 
@@ -61,6 +62,9 @@ pkgs.mkShell {
     # `cargo build` on MacOS.
     pkgs.libiconv
     pkgs.buildPackages.darwin.apple_sdk.frameworks.Security
+  ] ++ pkgs.lib.optionals withIntegration [
+    pkgs.cbtemulator
+    pkgs.google-cloud-bigtable-tool
   ];
 
   # Set TVIX_BENCH_NIX_PATH to a somewhat pinned nixpkgs path.