[stable/ambassador] Allow rbac to be namespaced

[naseemkullah]

What this PR does / why we need it:

Seldon Core would like to instead of deploy ambassador within it's helm chart, use the stable repo's ambassador chart as a dependency. One missing feature is the ability to allow rbac to be namespace-scoped rather than cluster-scoped.

This PR allows the end user to configure rbac to be namespace scoped if they so desire.

Which issue this PR fixes

Please see:
SeldonIO/seldon-core#445

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• DCO signed
• Chart Version bumped
• Variables are documented in the README.md

[naseemkullah]

cc @kflynn @Flydiverny

[steven-sheehy]

/ok-to-test
/assign @Flydiverny

[k8s-ci-robot]

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/ok-to-test
/assign @Flydiverny

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[Flydiverny]

/assign @Flydiverny

[Flydiverny]

Nice! was thinking about whether to change anything for rbac if you run ambassador in a single namespace or so :)
/approve

[naseemkullah]

Thanks @Flydiverny !

[Flydiverny]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Flydiverny, naseemkullah

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