Add support for a pre-smart-pull hook

[sufyanadam]

User can create an executable script in .git/hooks/smart-pull-pre-fetch that will be executed just before a fetch.

Example: There are tags in remote that need to be cleaned out. One team member cleans them out but then they come back the next time someone else pushes a local tag before syncing local tags to remote. A solution to this problem is to create a smart-pull-pre-fetch hook that syncs local tags to remote tags, so that old tags previously deleted on remote don't come back.