[Shared UX] Markdown Component

[rshen91]

Summary

Relating to #141166 taking considerations from instances of markdown etc in Kibana for this Shared UX Markdown component using EuiMarkdownEditor and EuiMarkdownFormat.

For places that previously used MarkdownSimple both implementations are supported:

    toastNotifications.addWarning({
      title: warnTitle,
      text: toMountPoint(<Markdown readOnly markdownContent={warnDescription} />),
    });

which was previously:

 toastNotifications.addWarning({
      title: warnTitle,
      text: toMountPoint(<MarkdownSimple readOnly>{warnDescription}</MarkdownSimple>),
  });

If readOnly is not passed, then the Markdown component will be passed as EuiMarkdownEditor.

openLinksInNewTab is removed due to lack of support in Github Flavored Markdown but workaround from @chandlerprall implemented in commit 66ed116

Checklist

Delete any items that are not applicable to this PR.

• 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 cross-browser compatibility

[rshen91]

Adding openInNewTab support based on Chandler's work in https://codesandbox.io/s/relaxed-yalow-hy69r4?file=/demo.js in commit 66ed116

[kibana-ci]

💚 Build Succeeded

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• Commit: fbdd574
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Metrics [docs]

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
@kbn/shared-ux-markdown	-	2	+2
@kbn/shared-ux-markdown-mocks	-	31	+31
total			+33

Public APIs missing exports

Total count of every type that is part of your API that should be exported but is not. This will cause broken links in the API documentation system. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats exports for more detailed information.

id	before	after	diff
@kbn/shared-ux-markdown	-	1	+1
@kbn/shared-ux-markdown-types	-	1	+1
total			+2

Unknown metric groups

API count

id	before	after	diff
@kbn/shared-ux-markdown	-	2	+2
@kbn/shared-ux-markdown-mocks	-	32	+32
total			+34

History

• 💔 Build #81136 failed bb9ccf8
• 💚 Build #80762 succeeded 4ac5528
• 💔 Build #80720 failed 961ef04
• 💚 Build #80561 succeeded ea928d2
• 💚 Build #80519 succeeded 4bc7e51
• 💚 Build #80469 succeeded afabced

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @rshen91