feat: add plugin netlify-plugin-flutter at version 1.1.0

[bencevans]

Thanks for contributing the Netlify plugins directory!

Are you adding a plugin or updating one?

• Adding a plugin
• Updating a plugin

Have you completed the following?

• Read and followed the plugin author guidelines.
• Included all required fields in your entry.
• Tested the plugin locally and on Netlify, using the plugin version stated in your entry.

Test plan
Please add a link to a successful public deploy log using the stated version of the plugin. Include any other context reviewers might need for testing.

https://app.netlify.com/sites/flutter-plugin/deploys/62601825c3a1f70008d0c006

[ascorbic]

Thanks!