Docs: Move multiple controllers FAQ.

[longwuyuan]

What this PR does / why we need it:

• The howto steps for multiple-instances of the controller is buried in the migration guide
• This PR moves the howto-steps for multiple-instance of the controller to the FAQ section

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• CVE Report (Scanner found CVE and adding report)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation only

Which issue/s this PR fixes

• No issue created

How Has This Been Tested?

• Its just docs

Checklist:

• [z] My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added unit and/or e2e tests to cover my changes.
• All new and existing tests passed.

cc @tao12345666333 @strongjz @Gacko @rikatz

/triage accepted
/area docs
/kind documentation

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[Gacko]

/triage accepted
/kind documentation
/priority backlog
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Gacko, longwuyuan

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• docs/OWNERS [Gacko,longwuyuan]

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[Gacko]

/retitle Docs: Move multiple controllers FAQ.

[Gacko]

/cherry-pick release-1.10

[k8s-infra-cherrypick-robot]

@Gacko: new pull request created: #11409

In response to this:

/cherry-pick release-1.10

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