[prometheus-thanos] Add grpc port to thanos receiver service

[iemre]

Signed-off-by: Emre Kartoglu iemrek@gmail.com

What this PR does / why we need it:

The Service definition for Thanos Receiver did not have the grpc port listed. The port is there in the values file, and I can't think of a reason why it shouldn't be in the Service definition too, therefore I'm treating this change as a patch.

Notes for the reviewer:

I've tested the changes on my local kind cluster.

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [x] DCO signed
• [x] Chart Version bumped (if the pr is an update to an existing chart)
• [x] Variables are documented in the README.md
• [x] Title of the PR starts with chart name (e.g. [fluentd-elasticsearch])