docs: fix Docker config paths for v2 documentation

- Correct config mount path from /etc/flipt/config.yaml to /etc/flipt/config/default.yml
- Add comprehensive persistent storage documentation with full configuration example
- Update login-with-github guide to use correct mount paths and include persistent storage
- Ensure consistency across all v2 Docker examples

Fixes #371

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Mark Phelps <[email protected]>

Author: claude[bot]

docs/v2/guides/operations/authentication/login-with-github.mdx

@@ -78,11 +78,13 @@ The last bit of configuration is the session details. In order for the browser t
 ```bash
 docker run -it --rm \
   -p 8080:8080 \
-  -v "$(pwd)/config.yml:/config.yml" \
-  flipt/flipt:v2 ./flipt server --config /config.yml
+  -p 9000:9000 \
+  -v $HOME/flipt:/var/opt/flipt \
+  -v "$(pwd)/config.yml:/etc/flipt/config/default.yml" \
+  docker.flipt.io/flipt/flipt:v2
 ```
 
-This will mount the `config.yml` as a volume in the container, and Flipt will use that configuration as it's provided as a command line flag option.
+This will mount both the data directory for persistent storage and the `config.yml` configuration file into the container at the standard location.
 
 ### 3. Navigate to the Flipt UI
 

docs/v2/installation.mdx

@@ -103,17 +103,33 @@ application.
 
 ### Configuration
 
-A default configuration file is included within the image. To supply a custom configuration, update the `docker run` command to mount your local configuration into the container:
+A default configuration file is included within the image. To supply a custom configuration, update the `docker run` command to mount your local configuration into the container.
+
+The example below shows how to configure Flipt v2 with both persistent storage and a custom configuration file:
 
 ```console
 docker run -d \
     -p 8080:8080 \
     -p 9000:9000 \
     -v $HOME/flipt:/var/opt/flipt \
-    -v $HOME/flipt/config.yaml:/etc/flipt/config.yaml \
+    -v $HOME/flipt/config.yaml:/etc/flipt/config/default.yml \
     docker.flipt.io/flipt/flipt:v2
 ```
 
+In this configuration:
+- `$HOME/flipt:/var/opt/flipt` mounts the host directory for persistent data storage
+- `$HOME/flipt/config.yaml:/etc/flipt/config/default.yml` mounts your custom configuration file
+
+Your `config.yaml` should specify the full path for storage:
+
+```yaml
+storage:
+  default:
+    backend:
+      type: local
+      path: /var/opt/flipt
+```
+
 ## Homebrew
 
 You can install Flipt v2 using [Homebrew](https://brew.sh/) on macOS and Linux.