fix(MessageBox): Adjust spacing

[rebeccaalpert]

WelcomePrompt had spacing on top, while MessageBox didn't. I moved the spacing onto the parent since WelcomePrompt is optional. Also adding prop to control position of MessageBox content, and adding a demo for how the removal interaction could work. Design wants to demonstrate the welcome message going away when new messages are sent.

See https://virtual-assistant-pr-virtual-assistant-323.surge.sh/patternfly-ai/chatbot/ui/react/welcome-interaction/ and https://virtual-assistant-pr-virtual-assistant-323.surge.sh/patternfly-ai/chatbot/ui#welcome-interaction.

Getting a screenshots error; will debug and add those later:

npm run docs:screenshots

> @patternfly/virtual-assistant@1.0.0-prerelease.0 docs:screenshots
> pf-docs-framework screenshots --urlPrefix http://localhost:5001

/Users/ralpert/Documents/virtual-assistant/node_modules/puppeteer-cluster/dist/Worker.js:41
                        throw new Error('Unable to get browser page');
                              ^

Error: Unable to get browser page
    at Worker.<anonymous> (/Users/ralpert/Documents/virtual-assistant/node_modules/puppeteer-cluster/dist/Worker.js:41:31)
    at Generator.next (<anonymous>)
    at fulfilled (/Users/ralpert/Documents/virtual-assistant/node_modules/puppeteer-cluster/dist/Worker.js:5:58)

Node.js v22.6.0
npm error Lifecycle script `docs:screenshots` failed with error:
npm error code 1
npm error path /Users/ralpert/Documents/virtual-assistant/packages/module
npm error workspace @patternfly/virtual-assistant@1.0.0-prerelease.0
npm error location /Users/ralpert/Documents/virtual-assistant/packages/module
npm error command failed
npm error command sh -c pf-docs-framework screenshots --urlPrefix http://localhost:5001

[patternfly-build]

Preview: https://virtual-assistant-pr-virtual-assistant-323.surge.sh

A11y report: https://virtual-assistant-pr-virtual-assistant-323-a11y.surge.sh

[github-actions[bot]]

:tada: This PR is included in version 2.1.0-prerelease.16 :tada:

The release is available on:

• GitHub release
• npm package (@prerelease dist-tag)

Your semantic-release bot :package::rocket: