DOCS-679 - Kanso opt-out GA

[kimsauce]

Purpose of this pull request

Kanso - New UI becomes the default UI at sign-in (instead of Classic UI).

Select the type of change

• Minor Changes - Typos, formatting, slight revisions
• Update Content - Revisions, updating sections
• New Content - New features, sections, pages, tutorials
• Site and Tools - .clabot, version updates, maintenance, dependencies, new packages for the site (Docusaurus, Gatsby, React, etc.)

Ticket (if applicable)

https://sumologic.atlassian.net/browse/DOCS-679

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[jpipkin1]

Looks great, @kimsauce!

[kimsauce]

Appreciate your feedback, @DeLonga! Your suggestion to clarify the UI improvements and update the retirement messaging made a big difference. cc: @kevin-sumo