pubsub/pstest: Support for subscription filters

[andreas-lindfalk]

Is your feature request related to a problem? Please describe.
Nor the pubsub emulator or pstest support subscription filters, making it impossible to integrationtest a pubsub setup making use of filters today.

Describe the solution you'd like
There is an embryo in pstest for filters, they can be set and updated and there is a filterMsgs func where filters could be applied according to the documented filter rules. In other words, implement support for subscription filters in pstest

Describe alternatives you've considered
As mentioned, the pubsub emulator does not support subscription filters either…

Additional context
I could take a stab at implementing this if you peps at Google have limited resources ;)

[hongalex]

Hey, thanks for bringing this up. Yeah unfortunately supporting filtering in either the emulator and the fake is not a high priority item currently.

If you have a PR to send over, I would be happy to look it over and find a way to get that merged in. Would require signing a CLA

[zezhehh]

Hey, thanks for bringing this up. Yeah unfortunately supporting filtering in either the emulator and the fake is not a high priority item currently.

If you have a PR to send over, I would be happy to look it over and find a way to get that merged in. Would require signing a CLA

Just submitted a PR. It would be great if you could take a look :D
#9015