Adds unit tests for the config file read/write helpers.
It also uncovered a bug in how viper handles writing a config file when a config file path is set
directly. This required a workaround in our init logic when we are using a custom config file name.
This commit does the following:
- Refactors the init logic into a InitConfig helper
- Adds a unit test to validate basic ReadRepoConfig behavior
- Adds a unit test that uses WriteReadConfig to write config and ReadRepoConfig to read it
