feat: ftl new and ftl init updates

[wesbillman]

Fixes #3924

Automatically create project folder and update help:

Usage: ftl init <name> [<dir>] [flags]

Initialize a new FTL project.

Examples:

    ftl init myproject        # Creates a new folder named "myproject" and initializes it
    ftl init myproject .      # Initializes the current directory as "myproject"
    ftl init myproject custom # Creates a folder named "custom" and initializes it as "myproject"

Creating a new ftl project will provide some help to the user as well:

ftl init myproject

Successfully created FTL project 'myproject' in myproject

To get started:
  cd myproject
  ftl dev

And update docs site:

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

frontend/cli/cmd_init.go:60

• The error message should include the directory name to provide more context. Suggestion: return fmt.Errorf("failed to create directory %s: %w", i.Dir, err)

return fmt.Errorf("failed to create directory: %w", err)