[CP-208] Add MeteringService (#138)

* Add MeteringService

- `ListMonthlyMeterings` returns a summary of the usage per month.
- `ListMeterings` returns the details of the usage for a specific month.

* Address feedback

* Address more feedback

* Update generated code

* Remove TODO item

Author: Toni Reina

.github/actions/spelling/allow.txt

@@ -1,33 +1,34 @@
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 buf
-protobuf
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 cel
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 jwt
 jwts
-oneof
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 multivector
-idf
-CIDRs
-upsert
-gpu
 nvidia
-amd
-linode
+oneof
 openshift
-gibibytes
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-timeseries
-vcpu
-civo
-CLIs
-Hcloud
-OVHCLOUD
+protobuf
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 scaleway
 snapclass
 stackit
+timeseries
+upsert
+vcpu
 vultr