Add a more user-friendly way to select namespaces in Jira Connect App

Currently, when adding a namespace, we just show a text input where the user can type in a namespace / group path.

It would be better if we can show an autocomplete / searchable dropdown here where users can select the namespace they want to add.

These namespaces are those that the user has access to add and have the appropriate license to integrate with Jira.

Current state

Proposal

• Reduce uncertainty for the user by exposing a list of available namespaces
• Add a way to filter the list of namespaces
• Surface the process of selecting a namespace using a modal to simplify the setup process (See Pajamas documentation for reference)
• Leverage the existing New Fork flow behavior

See Designs section for mockups and specs.

See (#232727 (closed)) for an example of entire flow installation flow.