feat: base quickstart on remote existing target

[adaam2]

This PR adds the ability to bootstrap a new target using a pre-existing specification hosted on Speakeasy's registry. The CLI will now show the most recent 5 targets that have been interacted with (based on the CLI event stream).

If there are any recent target candidates in the workspace, then the user will be presented with the option to choose from an existing SDK or create from scratch at the beginning of Quickstart. If there are no previous generations in a workspace, then the existing "new user" flow will be shown where the user can enter a filepath to a spec:

Then selecting from the list of recent SDKs:

(n.b the look and feel of the select list in the 2nd screenshot will change / look much better once the corresponding charmbracelet/huh#424 pr has been merged)

The end result is that a new workflow file is created that references the existing Registry URI for the spec from the previous target

Next steps

• Try and re-use as much of the prior target's gen.yaml

[simplesagar]

+1 for the concept

[adaam2]

@ryan-timothy-albert I've updated this now so that it checks if a namespace has a main tag. If so, it will include it in the "recents" list shown to the user.