add_namespace_in_snmp_integration

[kisungyi92]

What does this PR do?

This PR is for adding namespace parameter in snmp.d/conf.yaml

Motivation

When the customer connect network devices with same IP where their private network is different, the agent can't recognize it's different device.
We currently have an option - network_devices.namespace but this is more of global option but we are still accepting the instance level parameter namespace

• reference : https://github.com/DataDog/datadog-agent/blob/4862c809541337b2577154ad3c0d8a7cb0c61e69/pkg/snmp/snmp.go#L199

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[FlorianVeaux]

Hey this is by design and shouldn't be updated. A single agent should always have a single namespace.
Namespace is here to disambiguate between two private networks where private IP collides, and for which you have one Agent in each network.
If you have the IP 10.0.0.200 which collides in two different namespaces, it's impossible for the same Agent ro reach the two device if they share the same address