add Kata Containers as a valid runtime

[egernst]

Is this a request for help?:

No.

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Is this an ISSUE or FEATURE REQUEST? (choose one):

This is a FEATURE REQUEST

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What version of acs-engine?:

All of them

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Would love to s/Clear/Kata for original Clear Containers PR, adding support for Kata Containers (kata-runtime). Eventually we will want to consider deprecating Clear Containers (cc-runtime).

How to reproduce it (as minimally and precisely as possible):

Grep for Kata

Anything else we need to know:

I'm reviewing the original PRs from @jessfraz which added Clear Container support as well as ACS-engine now, and hope to submit an initial PR to add this support.

[egernst]

thx @CecileRobertMichon - I think I'm not part of the "organization", so could not self-assign.

[CecileRobertMichon]

#3465