Add attribute tags

[hofbi]

Many people might want to tag their cuda targets with gpu or something, hence it would be nice to add a tags attribute to cuda_libary and cuda_object

[cloudhan]

Do we need to manually add it as an attribute? https://bazel.build/reference/be/common-definitions?hl=en#common-attributes claims it is common to all build rules, I am not sure if it apply to user defined rules or not.

[hofbi]

I expected that this should work by default but for some reason passing a tag does not work.

[ryanleary]

@hofbi do you have a repro for this? I'll confirm tomorrow, but I'm pretty sure we have cuda targets with tags in some of our projects working as expected.

[hofbi]

Sorry, nothing that I can share. Let me double check, maybe it works meanwhile.

[hofbi]

Looks like it is working now. We can close this one.