restructure project to allow more artifacts to be built (e.g. a CLI)

This commit merely moves files around to form this structure:

```
client/              # A ChaosSearch client library
terraformprovider/   # A Terraform provider (uses client)
cli/                 # A CLI (uses client)
```

Author: benzaita

.github/workflows/release.yml

@@ -11,7 +11,7 @@
 # You will need to pass the `--batch` flag to `gpg` in your signing step 
 # in `goreleaser` to indicate this is being used in a non-interactive mode.
 #
-name: release
+name: release Terraform provider
 on:
   push:
     tags:
@@ -44,6 +44,7 @@ jobs:
         with:
           version: latest
           args: release --rm-dist
+          workdir: terraformprovider
         env:
           GPG_FINGERPRINT: ${{ steps.import_gpg.outputs.fingerprint }}
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}