Change ConfigUrl() (and like methods) to ConfigRemotePath()

Since we're trying to abstract where and how butler can retrieve configuration files, then let's rename the helper methods which referenced ConfigUrl, to somethign like ConfigRemotePath, which would be more inline to where we want to go.

For example. The manager option has a method called `AppendPrimaryConfigUrl()`. Let's change that to something like `AppendPrimaryConfigRemotePath()` The other helper functions should be changed as well.

May as well tweak the references for the local path methods as well.
eg: `ManagerOpts::AppendPrimaryConfigFile()` -> `ManagerOpts::AppendPrimaryLocalConfigFile()`.

yeah.

Start by searching the Go repository for ConfigUrl and the example methods ManagerOpts::AppendPrimaryConfigUrl and ManagerOpts::AppendPrimaryConfigFile. Trace all related helper definitions and references, then confirm that the remote-path and local-path names are consistent everywhere and that the project still builds and its tests pass.

Written by the indexing model from the issue text.