chore(scripts): add release autoversion to bump releases in docs (#13063)

This PR adds a command to bump versions in docs/markdown.

This is still standalone and needs to be wired up.

For now, I'm planning on putting this in `scripts/release.sh` (checkout main -> autoversion (this command) -> commit -> submit PR).

It would be pretty neat to make it a GH actions that's triggered on release though, something for the future.

Part of #12465

scripts/release/testdata/autoversion/docs/kubernetes.md

@@ -0,0 +1,25 @@
+# Some documentation
+
+1. Run the following command to install the chart in your cluster.
+
+   For the **mainline** Coder release:
+
+   <!-- autoversion(mainline): "--version [version]" -->
+
+   ```shell
+   helm install coder coder-v2/coder \
+       --namespace coder \
+       --values values.yaml \
+       --version 2.10.0
+   ```
+
+   For the **stable** Coder release:
+
+   <!-- autoversion(stable): "--version [version]" -->
+
+   ```shell
+   helm install coder coder-v2/coder \
+       --namespace coder \
+       --values values.yaml \
+       --version 2.9.1
+   ```

scripts/release/testdata/autoversion/docs/kubernetes.md.golden

@@ -0,0 +1,25 @@
+# Some documentation
+
+1. Run the following command to install the chart in your cluster.
+
+   For the **mainline** Coder release:
+
+   <!-- autoversion(mainline): "--version [version]" -->
+
+   ```shell
+   helm install coder coder-v2/coder \
+       --namespace coder \
+       --values values.yaml \
+       --version 2.11.1
+   ```
+
+   For the **stable** Coder release:
+
+   <!-- autoversion(stable): "--version [version]" -->
+
+   ```shell
+   helm install coder coder-v2/coder \
+       --namespace coder \
+       --values values.yaml \
+       --version 2.9.4
+   ```