docs: added epp standalone user guide

[capri-xiyue]

What type of PR is this?

/kind documentation
What this PR does / why we need it:
Added use case for epp standalone mode

Which issue(s) this PR fixes:

Fixes #2146

Does this PR introduce a user-facing change?:

None

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[capri-xiyue]

assign @kfswain

[capri-xiyue]

assign @ahg-g