New dcc.Markdown prop 'link_target'

[adrianoesch]

This PR is adding the prop link_target to dcc.Markdown component, analogous to the behaviour in datatable and thereby closing #1827.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • Figure out react-markdown integration
  • Add necessary props and documentation string
• I have run the tests locally and they passed (though only dash-core-components markdown test).
• I have added a test.

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • this GitHub #PR number updates the dash docs
  • here is the show and tell thread in Plotly Dash community

[alexcjohnson]

Beautiful, with a test and everything 😍
Just add a changelog entry and we'll merge.

[adrianoesch]

Great! Just added the changelog.

[alexcjohnson]

The Percy tests here are showing a problem (Python errors showing up in the browser as a raw string rather than rendered HTML) that I suspect is due to the latest Werkzeug release. It certainly isn't anything you did in this PR @adrianoesch, but I don't want to merge until we fix it so we don't lose the correct Percy baselines. @T4rk1n can you take a look at addressing this?

[T4rk1n]

@alexcjohnson The doctype changed to all lowercase in werkzeug 2.1.2, I modified the check to accommodate all case in #2035

[alexcjohnson]

💃