Utility functions and specification of EPP command line flags

[elevran]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Allows definition of command line flags in declarative and centralized manner.
Previously split between cmd/epp/runner/runner.go and pkg/epp/server/runserver.go and handling of deprecation was manual.

Which issue(s) this PR fixes:
Fixes #1932

Does this PR introduce a user-facing change?:

NONE

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: elevran
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[elevran]

/cc @ahg-g @kfswain @nirrozenbaum for early feedback. See #1932 for some additional context.
Is this reasonable (need and approach)?

If so, follow up commits on this PR (or I can split into smaller for easier review) can

• optionally move options.go to pkg/common and leave only cli_flags.go in pkg/epp?
• remove flag definitions and defaults (assuming no cut-n-paste errors on my end) from runner and runserver
• runner.go to use pass []flags to options.AddFlags instead of creating flags directly
• remove functions that are no longer needed (e.g., checking deprecated in runner, setting defaults from command line in datalayer/metrics, etc.)

[shmuelk]

Why not use generics here and have only one function?

That will also cover integers and other types....

[elevran]

That's certainly possible and would genralize and simplify the code somewhat.
Wanted to keep initial code simpler as mostly looking for feedback on whether this is useful before investing more time.