Track usage of --v2-debug usage and final --v2-debug changes

[aemous]

Description of changes:

• Usage of the new migration debug flag is tracked in the User-Agent header.
• Add support for the pager output breaking change, with resolution determined by setting cli_pager config to the empty string.
• An environment variable exists as an alternative to the --v2-debug command line option
• A --no-v2-debug CLI option exists (boolean switch).
• The text "AWS CLI v2 MIGRATION WARNING" is updated to "AWS CLI v2 UPGRADE WARNING"
• Updated scalarparse runtime detection to only print warning if the user did not configure any setting for cli_timestamp_format.
• Replaced cloudformation deploy's warning's reliance on the service response: output it even if the changeset is non-empty.
• Updated warnings to give more guidance, especially retaining v1 behavior on v2
• Updated the binary-params-base64 use case. It does not need to be prefixed with file://.
• Replace use of uni print outside of customizations with print.

Description of tests:

• Ran and passed all unit and functional tests.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.28571% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (debug-migration@db28bd8). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
awscli/clidriver.py	66.66%	1 Missing ⚠️
awscli/customizations/cloudformation/deploy.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##             debug-migration    #9810   +/-   ##
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  Coverage                   ?   93.30%           
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  Files                      ?      209           
  Lines                      ?    16910           
  Branches                   ?        0           
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  Hits                       ?    15778           
  Misses                     ?     1132           
  Partials                   ?        0           

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