[otel-agent] allow setting cluster name

[povilasv]

Description

Allow users to easily set clusterName.

Tested with kind cluster:

helm install --values new-values.yaml otel-agent .  

My example generated:

        resource/metadata:
          attributes:
          - action: upsert
            key: k8s.cluster.name
            value: 'kind'
          - action: upsert
            key: cx.otel_integration.name
            value: coralogix-otel-agent-helm

Fixes https://coralogix.atlassian.net/browse/ES-21

How Has This Been Tested?

Checklist:

• I have updated the relevant Helm chart(s) version(s)
• I have updated the relevant component changelog(s)
• This change does not affect any particular component (e.g. it's CI or docs change)