Add directoryIndex and documentRoot to InAppLocalhostServer option

[fa0311]

Connection with issue(s)

How is the feature useful

Less hassle when loading existing html for websites.

Testing and Review Notes

final InAppLocalhostServer localhostServer = InAppLocalhostServer(
  port: 8080,
  documentRoot: "./assets/website/",
  directoryIndex: "index.html",
);

Screenshots or Videos

To Do

• double check the original issue to confirm it is fully satisfied
• add testing notes and screenshots in PR description to help guide reviewers
• request the "UX" team perform a design review (if/when applicable)

[pichillilorenzo]

Thanks! @all-contributors please add @fa0311 for code

[allcontributors]

@pichillilorenzo

I've put up a pull request to add @fa0311! 🎉