Add destination directory as argument to swift package init

[eliperkins]

Closes #7791

This allows for specifying the directory to create a new package within. If no argument is supplied, matching the current supported command options, then the package will be created in the current working directory. If an argument is supplied, then the package will be created in the directory at the path specified.

Motivation:

The goal is to make the creation of new packages more predictable based on the arguments passed in, as well as to give more control to developers to specify the location of new packages, rather than relying on current working directory contexts and forcing the developer to mkdir and cd a bunch while using this command.

Modifications:

• Added a single argument to swift package init to take in the directory to create the package at
• Modified the progress print statements during creation to specify the relative directories that the package is being created in

Result:

• The existing syntax for commands to swift package init is unchanged, where if no arguments are specified, the package will be created in the current working directory.
• If an argument is specified, the package will be created at that destination path instead.