Refactor metrics

[KalmanMeth]

Description

Refactor Metrics code so that it is common for Prometheus and OpenTelemetry metrics. This removes duplicate code and now gives us the implementation for OpenTelemetry histograms.

Dependencies

n/a

Checklist

If you are not familiar with our processes or don't know what to answer in the list below, let us know in a comment: the maintainers will take care of that.

• [ ] Will this change affect NetObserv / Network Observability operator? If not, you can ignore the rest of this checklist.
• [ ] 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).

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 68.00000% with 80 lines in your changes are missing coverage. Please review.

Project coverage is 67.06%. Comparing base (5e89c89) to head (9b8e42d). Report is 11 commits behind head on main.

Files	Patch %	Lines
...ipeline/encode/opentelemetry/encode_otlpmetrics.go	23.63%	42 Missing :warning:
pkg/pipeline/encode/metrics_common.go	79.59%	22 Missing and 8 partials :warning:
pkg/pipeline/encode/encode_prom.go	83.33%	5 Missing and 3 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #590 +/- ## ========================================== + Coverage 66.04% 67.06% +1.02% ========================================== Files 103 104 +1 Lines 7509 7405 -104 ========================================== + Hits 4959 4966 +7 + Misses 2256 2143 -113 - Partials 294 296 +2 ``` | [Flag](https://app.codecov.io/gh/netobserv/flowlogs-pipeline/pull/590/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/flowlogs-pipeline/pull/590/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=netobserv) | `67.06% <68.00%> (+1.02%)` | :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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[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[jotak]

/lgtm