feat: accordion: enable custom summary layout using full width

[dkilgore-eightfold]

SUMMARY:

Enables custom full width Accordion AccordionSummary layouts, and adds more discreet custom props. Prior to this change, implementation of certain layouts was difficult because the header could not be easily made to fill the remaining space of the Accordion without using custom class names and css paths.

• Adds fullWidth prop to AccordionSummary, setting the header and its container flex to 1 when enabled
• Adds listStyle to List component to support inline customizing
• Gives the Accordion a min-width so it doesn't clip its content when reflow in small screens
• Adds a gap to the summary styles
• Renames some internal variables
• Adds onIconButtonClick callback
• Passes iconButtonProps to the Button
• Alphabetizes props
• Adds Custom story

accordionReflow.mp4

JIRA TASK (Eightfold Employees Only):

ENG-80058

CHANGE TYPE:

• Bugfix Pull Request
• Feature Pull Request

TEST COVERAGE:

• Tests for this change already exist
• I have added unittests for this change

TEST PLAN:

Pull the PR branch and run yarn and yarn storybook. Verify the Accordion stories behave as expected.

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