Enhancement: New git actions to disable or require a commit message

[estruyf]

This issue is related to #610, but will only implement the following features:

• Define which branches the git actions should be disabled
• Define which branches require a commit message before syncing
• Adding a fetch changes button

New settings

• frontMatter.git.disableOnBranches - string[]: set the names of the branches that should disable the sync action
• frontMatter.git.requiresCommitMessage - string[]: set the names of the branches to require a commit message