NETOBSERV-1533: refine metrics for dashboard creation

[jotak]

• Use just two shared metrics for eviction counters: on for eviction events and one for flows; shared across ringbuf/map implementations and labelled as such
• Report more errors via metrics

[openshift-ci-robot]

@jotak: This pull request references NETOBSERV-1533 which is a valid jira issue.

Warning: The referenced jira issue has an invalid target version for the target branch this PR targets: expected the story to target the "4.16.0" version, but no target version was set.

In response to [this](https://github.com/netobserv/netobserv-ebpf-agent/pull/281): >- Use just two shared metrics for eviction counters: on for eviction events and one for flows; shared across ringbuf/map implementations and labelled as such >- Report more errors via metrics > Instructions for interacting with me using PR comments are available [here](https://prow.ci.openshift.org/command-help?repo=netobserv%2Fnetobserv-ebpf-agent). If you have questions or suggestions related to my behavior, please file an issue against the [openshift-eng/jira-lifecycle-plugin](https://github.com/openshift-eng/jira-lifecycle-plugin/issues/new) repository.

[jotak]

@msherif1234 as I'm working on the dashboard and I'm bringing a few changes here. Here's a screenshot of what I get with these metrics:

Some text counters in the top bar:

Some ebpf stats:

(something looks wrong in the eviction rate when it evicts because of full map)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 69.10569% with 38 lines in your changes are missing coverage. Please review.

Project coverage is 36.26%. Comparing base (b3c02b8) to head (4a58e68). Report is 2 commits behind head on main.

Files	Patch %	Lines
pkg/agent/agent.go	35.48%	20 Missing :warning:
pkg/ebpf/tracer.go	0.00%	9 Missing :warning:
pkg/flow/tracer_ringbuf.go	50.00%	5 Missing :warning:
pkg/exporter/kafka_proto.go	50.00%	2 Missing :warning:
pkg/exporter/grpc_proto.go	90.90%	1 Missing :warning:
pkg/flow/account.go	93.33%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #281 +/- ## ========================================== + Coverage 36.08% 36.26% +0.18% ========================================== Files 42 42 Lines 3786 3794 +8 ========================================== + Hits 1366 1376 +10 + Misses 2342 2340 -2 Partials 78 78 ``` | [Flag](https://app.codecov.io/gh/netobserv/netobserv-ebpf-agent/pull/281/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=netobserv) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/netobserv/netobserv-ebpf-agent/pull/281/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=netobserv) | `36.26% <69.10%> (+0.18%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=netobserv#carryforward-flags-in-the-pull-request-comment) to find out more.

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[msherif1234]

/lgtm

[github-actions[bot]]

New image: quay.io/netobserv/netobserv-ebpf-agent:12b1753

It will expire after two weeks.

To deploy this build, run from the operator repo, assuming the operator is running:

USER=netobserv VERSION=12b1753 make set-agent-image

[jotak]

@msherif1234 I think this task is done I've got all metrics needed to build a nice dashboard - can you take a second look & review please?

[github-actions[bot]]

New image: quay.io/netobserv/netobserv-ebpf-agent:26076c3

It will expire after two weeks.

To deploy this build, run from the operator repo, assuming the operator is running:

USER=netobserv VERSION=26076c3 make set-agent-image

[msherif1234]

overall looks great to me small comments/questions inline up to you to address nothing critical /lgtm

[jotak]

/approve

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

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