Add optional tag to ELB name field

[sedefsavas]

What this PR does / why we need it:
The field is optional due to omitempty tag but to have same convention everywhere added the optional tag.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

Checklist:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

Release note:

NONE

[k8s-ci-robot]

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[sedefsavas]

/lgtm
/approve

[k8s-ci-robot]

@sedefsavas: you cannot LGTM your own PR.

In response to this:

/lgtm
/approve

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sedefsavas

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