Add skipHookPrefix to config

allows a user to specify a commit message prefix that will tell lazygit to skip
the pre-commit hook. This defaults to WIP. Setting it to the empty string will
disable the feature.

So if my message goes 'WIP: do the thing' then the pre-commit hook will not run

docs/Config.md

@@ -21,6 +21,7 @@
     merging:
       # only applicable to unix users
       manualCommit: false
+    skipHookPrefix: WIP
   update:
     method: prompt # can be: prompt | background | never
     days: 14 # how often an update is checked for