* Simplify BATS test Golang code
* Update plugin add test to new command format
* Correctly set `ASDF_DATA_DIR` for BATS tests
* Rename `PluginAdd` function to `Add`
* Create `plugin.Remove` function
* Make plugin remove command invoke `plugin.Remove` function
* remove underscores from function names (addresses warnings from revive linter)
* create installMockPluginRepo function
* implement plugin list command
* Add go-git as a dependency
* Remove plugins dir from gitignore
* Move config code to config package
* Create validatePluginName function
* Create PluginDirectory function
* Create PluginExists function
* Implement PluginAdd function
* Add testify as a dependency
* Write test for PluginAdd happy path
