Move release-operator to tools/ folder

This has the following advantages:
1. It provides some implicit documentation on what release-operator is,
   making it easier to see at first glance what's relevant only inside
   this repository, and what's relevant to users.
2. It provides a place for adding more tools later, without creating a
   mess in the repository root.

.github/workflows/cd.yml

@@ -93,11 +93,11 @@ jobs:
         uses: Swatinem/rust-cache@v1
         with:
           key: release-operator-01
-          working-directory: ./release-operator
+          working-directory: ./tools/release-operator
 
       - name: Operator | Deduce
         id: release
-        working-directory: ./release-operator
+        working-directory: ./tools/release-operator
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           RELEASE_LABEL: release
@@ -130,7 +130,7 @@ jobs:
 
       - name: Release | Crates.io
         if: ${{ steps.release.outputs.release-detected == 'true' }}
-        working-directory: ./release-operator
+        working-directory: ./tools/release-operator
         env:
           RUST_LOG: info
         run: |

Cargo.toml

@@ -16,7 +16,7 @@ members = [
     "models/spacer",
     "models/star",
 
-    "release-operator",
+    "tools/release-operator",
 ]
 default-members = [
     "crates/fj-app",