impr: BKTCLT-34 Go client: add Prometheus metrics

[jonathan-gramain]

Add metrics when requests are processed, in order for them to be exposed by the API user and scraped by Prometheus.

[bert-e]

Hello jonathan-gramain,

My role is to assist you with the merge of this
pull request. Please type @bert-e help to get information
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Status report is not available.

[bert-e]

Incorrect fix version

The Fix Version/s in issue BKTCLT-34 contains:

• 7.10.14

Considering where you are trying to merge, I ignored possible hotfix versions and I expected to find:

• 7.10.14

• 8.1.11

Please check the Fix Version/s of BKTCLT-34, or the target
branch of this pull request.

[jonathan-gramain]

ping

[bert-e]

Request integration branches

Waiting for integration branch creation to be requested by the user.

To request integration branches, please comment on this pull request with the following command:

/create_integration_branches

Alternatively, the /approve and /create_pull_requests commands will automatically
create the integration branches.