enhance bbr helm chart to generalize cmd-line args

[nirrozenbaum]

What type of PR is this?

What this PR does / why we need it:
with the expected additions to bbr, this PR is enhancing helm chart to generalize cmd-line arg specification through the helm chart flags (same as done in epp helm chart)

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

None

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nirrozenbaum

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[shmuelk]

/lgtm