support enableremote of git repo changing eg autoenable=

support enableremote of git repo changing eg autoenable=

enableremote: Support enableremote of a git remote (that was previously set
up with initremote) when additional parameters such as autoenable= are
passed.

The enableremote special case for regular git repos is intended to handle
ones that don't have a UUID probed, and the user wants git-annex to
re-probe. So, that special case is still needed. But, in that special
case, the user is not passing any extra parameters. So, when there are
parameters, instead run the special remote setup code. That requires there
to be a uuid known already, and it allows changing things like autoenable=

Remote.Git.enableRemote changed to be a no-op if a git remote with the name
already exists. Which it generally will in this case.

Sponsored-by: Jack Hill on Patreon