🪟 🎉 Connector Builder Landing Page

[lmossman]

What

Resolves https://github.com/airbytehq/airbyte/issues/21490

Adds a landing page for the connector builder, which is shown if the user doesn't have any connector builder changes saved to browser local storage.

To return to this page after making changes, click the Reset All button in the bottom-left corner of the Builder.

How

As described in the issue, this PR only adds tiles for importing a YAML and starting from scratch. Start from scratch just opens a blank connector builder UI as normal.

The Import a YAML button only allows users to select a single .yaml file from their computer to upload. A few outcomes can occur here:

1. The uploaded file contains invalid YAML. In this case, we just show a Toast with the YAML validation error message and line number, which is auto-dismissed if they click the import button again.
2. The uploaded file contains valid YAML, but it can't be converted to Builder UI. In this case, we open the YAML in the YAML editor view of the connector builder.
3. The uploaded file contains valid YAML and can be converted to Builder UI. In this case, we open the Builder UI with the values filled in from the YAML.
   • In this case, the Connector Name is set to the titleCase version of the file name (minus the extension), e.g. poke_api.yaml would result in the connector name set to Poke Api