NETOBSERV-2435 fix background mode and update doc

[jpinsonneau]

Description

• Fix background mode issue (follow is not showing logs since the new UI was implemented)
• Update doc to add an example for metrics background

Example after running $ oc netobserv metrics --background:

$ oc netobserv follow
Checking dependencies... 
'yq' is up to date (version v4.45.1).
'bash' is up to date (version v5.2.37).
Starting network-observability-cli:
=====
Build version: unknown
Build date: unknown


------------------------------------------------------------------------
         _  _     _       _                       ___ _    ___
        | \| |___| |_ ___| |__ ___ ___ _ ___ __  / __| |  |_ _|
        | .' / -_)  _/ _ \ '_ (_-</ -_) '_\ V / | (__| |__ | | 
        |_|\_\___|\__\___/_.__/__/\___|_|  \_/   \___|____|___|

------------------------------------------------------------------------
time="2025-10-02T11:08:33Z" level=info msg="Log level: info\nOption(s): background"
time="2025-10-02T11:08:33Z" level=info msg="Running in background mode"
time="2025-10-02T11:08:33Z" level=info msg="Kernel version: 5.14.0-570.45.1.el9_6.x86_64"
time="2025-10-02T11:08:33Z" level=info msg="sum(rate(on_demand_netobserv_node_egress_bytes_total[2m]))"
time="2025-10-02T11:08:33Z" level=info msg="  No result"
time="2025-10-02T11:08:33Z" level=info msg="sum(rate(on_demand_netobserv_node_egress_packets_total[2m]))"
time="2025-10-02T11:08:33Z" level=info msg="  No result"
...
time="2025-10-02T11:10:03Z" level=info msg="sum(rate(on_demand_netobserv_node_egress_bytes_total[2m]))"
time="2025-10-02T11:10:03Z" level=info msg="  {} =>\n171675.09052430323 @[1759403100]"
time="2025-10-02T11:10:03Z" level=info msg="sum(rate(on_demand_netobserv_node_egress_packets_total[2m]))"
time="2025-10-02T11:10:03Z" level=info msg="  No result"

Dependencies

n/a

Checklist

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• Is this PR backed with a JIRA ticket? If so, make sure it is written as a title prefix (in general, PRs affecting the NetObserv/Network Observability product should be backed with a JIRA ticket - especially if they bring user facing changes).
• Does this PR require product documentation?
  • If so, make sure the JIRA epic is labelled with "documentation" and provides a description relevant for doc writers, such as use cases or scenarios. Any required step to activate or configure the feature should be documented there, such as new CRD knobs.
• Does this PR require a product release notes entry?
  • If so, fill in "Release Note Text" in the JIRA.
• Is there anything else the QE team should know before testing? E.g: configuration changes, environment setup, etc.
  • If so, make sure it is described in the JIRA ticket.
• QE requirements (check 1 from the list):
  • Standard QE validation, with pre-merge tests unless stated otherwise.
  • Regression tests only (e.g. refactoring with no user-facing change).
  • No QE (e.g. trivial change with high reviewer's confidence, or per agreement with the QE team).

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[jotak]

would be safer / best practice to have defer Unlock here ?

   defer mutex.Unlock()

[jpinsonneau]

Sure, I can address that in parallel if it's ok for you

That code was already there and not related to that fix

[jotak]

/lgtm
just a nice-to-have comment

[memodi]

/ok-to-test

[github-actions]

New image:
quay.io/netobserv/network-observability-cli:f3fe30a

It will expire after two weeks.

To use this build, update your commands using:

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[memodi]

/label qe-approved

[openshift-ci]

@jpinsonneau: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/integration-tests	b2f60d3	link	true	/test integration-tests

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