Documentation updates for the Ambassador Install process and to introduce CRD based config.

[cakuros]

What this PR does / why we need it:
This PR is intended to update the Ambassador Ingress configuration to the more current Emissary and Ambassador Edge Stack installation suggestions. It primarily updates the API version to v2 and introduces Custom Resource Definition based configuration, as well as a basic example on how to translate CRD configs to Annotations, for those who want to use the seldon.io/ambassador-config annotation.

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Changed primary image mirror from quay.io to docker.io.
Changed API version numbers in examples from v1 to v2.
Added more details on Ambassador feature capabilities.
Added some explanations to the custom configuration section to explain the difference between annotation-based config and CRD.
Removed old note regarding gRPC issues.
Added both Ambassador install options to the "Seldon Setup" notebook.

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[seldondev]

Hi @cakuros. Thanks for your PR.

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[seldondev]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[cakuros]

/assign @cliveseldon

[ukclivecox]

Thanks @cakuros