Add support for commit.template in commit message

[andriidrz]

Fills commit message with contents of file configured by commit.template Git setting

PR Description

A lot of organisations have their own commit styles. Sometimes they have dedicated commit file templates with task id/commit type etc.
Usually these files are stored in git configuration (please see https://git-scm.com/docs/git-config#Documentation/git-config.txt-committemplate)

Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• If a new UserConfig entry was added, make sure it can be hot-reloaded (see here)
• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc

[andriidrz]

Please let me know if we really need separate test for this feature