Add support for medialive single pipeline

[wizage]

Is your feature request related to a problem? Please describe. In live encoding system-design, cost and reliability are at odds. For professional broadcast content, like live sports, where distribution rights are measured in the millions, reliability, at any cost, is required. For other uses, like user-generated content, IoT, and small event streaming, _pretty reliable__ streaming is acceptable in return for lower cost.

To support both models, MediaLive released a single pipeline option. This option essentially reduces a channel to a single-az and input in return for a ~%50 discount on cost.

Describe the solution you'd like Add an option or default to single pipeline mode for users who are seeking cost reduction or only have a single source by setting "channelClass": "SINGLE_PIPELINE" in the channel templates we use as part of amplify video.

Additional context There may be additional ramifications of this feature across medialive -> mediapackage. Need to further evaluate any dependencies on input/output changes to channel template.

[wizage]

@smp Can you expand on this and give more context. Also should this be implemented with #2

[wizage]

Planned for #1