Log if grpc is accessor or mutator
Overview
An rpc can either be an accessor or a mutator.
In https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/24086 we needed to look at the mutating requests on specific Gitaly nodes, and we didn't have an easy way to filter for them. In https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/24086#note_1463213257 we had to get the list of mutators by greping the proto directory and then create a Elasticseach query DSL with a script.
Proposal
We already have logging fields like gprc.code
, grpc.method
. We should include grpc.operation
and have it be accessor
and mutator
so that we can easily filter for the types of operations