New flags for playbook backends with AWS examples

[chungers]

This PR

• Adds a new --accept-defaults flag to all dynamically generated playbook commands. This makes it possible to run a playbook with minimal, default values (as defined in the playbooks) without prompting the user. This makes it easy to use playbooks in a script.
• Adds a new --plugin flag for all dynamically generated playbooks that target the instanceProvision backend. This way, the user can specify which plugin to target if the plugin is named differently. The flag will override the default specified in the playbook yml, if provided.
• An updated aws playbook is included as part of examples. This will replace the content in docs/playbooks/intro/aws which needs update (long overdue -- see Fix playbooks after change to running all plugins in a single binary / single process #710). The examples include starting up on-demand or spot instances. I will be using this example to work towards new CICD where we will use infrakit to build and test itself on different cloud platforms.

Signed-off-by: David Chung [email protected]

[codecov]

Codecov Report

Merging #828 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master    #828      +/-   ##
=========================================
- Coverage   47.91%   47.9%   -0.02%     
=========================================
  Files          89      89              
  Lines        7943    7945       +2     
=========================================
  Hits         3806    3806              
- Misses       3776    3778       +2     
  Partials      361     361

Impacted Files	Coverage Δ
pkg/provider/aws/plugin/instance/monitor.go	0% <0%> (ø)	⬆️

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