[FEATURE REQUEST] Run HAProxy using dedicated user instead of root

[to-bar]

Is your feature request related to a problem? Please describe.
Before changes from #1586 we had HAProxy installed as OS package (deb/rpm). The package automatically created OS user and group haproxy.

We had automated tests to check the following:

• User "haproxy" is expected to exist
• User "haproxy" is expected to have login shell "/usr/sbin/nologin" or have login shell "/sbin/nologin"
• Group "haproxy" is expected to exist
• User "haproxy" is expected to belong to group "haproxy"
• User "haproxy" is expected to have home directory "/var/lib/haproxy"

Now there is no haproxy user.

# grep haproxy /etc/shadow
haproxy_exporter:!:18528::::::

# grep -A3 user /opt/runc/haproxy/config.json
"user": {
    "gid": 0,
    "uid": 0
}

Describe the solution you'd like
Add haproxy user and run the haproxy service as this user.

Describe alternatives you've considered
No alternatives.

Additional context
As a part of this task we should restore automated tests removed in #1692.

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DoD checklist

• Changelog
  • updated
  • not needed
• COMPONENTS.md
  • updated
  • not needed
• Schema
  • updated
  • not needed
• Backport tasks
  • created
  • not needed
• Documentation
  • added
  • updated
  • not needed
• Feature has automated tests
• Automated tests passed (QA pipelines)
  • apply
  • upgrade
  • backup/restore
• Idempotency tested
• All conversations in PR resolved
• Solution meets requirements and is done according to design doc
• Usage compliant with license

[seriva]

Not going todo anymore feature requests for Epiphany.