[ML] Transforms: Fix page layout

[walterra]

Summary

Part of #45352.

Fixes the overall page layout of the transform plugin to be in line with the rest of the Kibana Elasticsearch management section:

• Wraps the whole page in a panel
• Adds links to documentation
• Adds a subheading with description (transform list)
• Moves the refresh and create button to the table search section (transform list)

Transform List

Transform Wizard

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

• This was checked for cross-browser compatibility, including a check against IE11
• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: d4599fb

[alvarezmelissa87]

Gave this a test and LGTM ⚡️

[peteharverson]

LGTM

[walterra]

@elasticmachine merge upstream

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 534cc5b