Add support for buildx build secrets

[shanejbrown]

What does this PR do?

Add support to buildrunner for build secrets. For more info see: https://docs.docker.com/build/building/secrets/

What issues does this PR fix or reference?

Previous Behavior

New Behavior

Merge requirements satisfied?

• I have updated the documentation or no documentation changes are required.
• I have added tests to cover my changes.
• I have updated the base version in BASE_VERSION (if appropriate).

[shanejbrown]

There is a problem running examples/build/secrets/platforms-buildrunner.yaml in github actions but it does work on my local machine. I get this error when it is ran in github exec /bin/sh: exec format error. So I am excluding examples/build/secrets/platforms-buildrunner.yaml from being ran in tests. If this is a problem in our build environment we can revisit this error.

[bluesliverx]

There is a problem running examples/build/secrets/platforms-buildrunner.yaml in github actions but it does work on my local machine. I get this error when it is ran in github exec /bin/sh: exec format error. So I am excluding examples/build/secrets/platforms-buildrunner.yaml from being ran in tests. If this is a problem in our build environment we can revisit this error.

Interesting... I usually see that when I try to mix x86 images with ARM machines, etc, but I'm not sure how that would apply here.