Add default_branch feature

[CAMOBAP]

Subject of the issue

Currently, GitHub suggest renaming of default branch from master to main https://stevenmortimer.com/5-steps-to-change-github-default-branch-from-master-to-main/

But in ruby-git in many places master used as the default branch https://github.com/ruby-git/ruby-git/blob/master/lib/git/base.rb#L345

My proposal to add new method git.default_branch which will do git symbolic-ref refs/remotes/origin/HEAD | sed 's@^refs/remotes/origin/@@' master based on https://stackoverflow.com/a/44750379/902217

Your environment

• version of git and ruby-git 1.9.0
• version of ruby 2.6.7p197

Steps to reproduce

Expected behaviour

Have a possibility to get default branch

Actual behaviour

For now it's not possible to get default branch

[stale]

A friendly reminder that this issue had no activity for 60 days.

[ronan-mch]

This would be a very helpful change.

[ronaldtse]

GitHub has since changed the default branch to main, accompanied by most in the industry.

Is it possible to merge this feature soon? It’s been a year and a half. I wonder if others who use ruby-git simply switch to vanilla command line git due to this…

[jcouball]

PRs #636, #637, #638, and #639 addressed where ruby-git assumed 'master' as a default branch for various git commands.

PR #571 added Git.default_branch.