Better guidance when unable to upgrade templates

[itowlson]

If the user has templates installed with Spin 0.8 or earlier, they will have no info saved saying where they come from, and spin templates upgrade will not work. The current message is a bit misleading. This PR tweaks the experience as follows:

• User has no templates installed at all - standard "prompt to install the default set" experience:

$ spin templates upgrade
No template repositories found to upgrade

You don't have any templates yet. Would you like to install the default set?

• User has templates, but none of them have origin information - point them in the right direction to perform an incantatory upgrade:

$ spin templates upgrade
No template repositories found to upgrade

Your template repositories were either:
* Installed from a directory; or
* Installed using an older version of Spin
To upgrade them, run `spin templates install --upgrade` with the --git or --dir option

Very open to bikeshedding wordsmithing on that new text.

Signed-off-by: itowlson ivan.towlson@fermyon.com