Raise an error if two plugins try to set the same key with different values

## Description

As more plugins are added to chalk, it is likely that they might be attempting to set the same value / key used by another plugin. For instance, the `cloudMetadata` plugin sets `_OP_CLOUD_PROVIDER_SERVICE_TYPE`, however the `ecsMetadata` plugin might choose to do so as well. These plugins might try to set the same value or might set different values, and worse they might choose to re-use a key that is used by another plugin in a completely different way. We can expose a common utility to set values that warns if plugins set different values for a given key, and potentially require plugins to register what keys they set, so that we can surface this information in documentation, as well as detect possible conflicts.

No files, tests, or entry points are named. Start by locating how plugins set shared keys and review the existing plugin architecture; done should include a common setting path that detects conflicting values and surfaces the conflict as an error or warning.

Written by the indexing model from the issue text.