Fix the image reference for prod: from v1.3.0 to 1.3.0 (#669)

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## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
The following PR fixes the docs and the image reference for prod since
they don't expect to have the v prefix there.

## How Has This Been Tested?
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tested? -->

## Breaking Changes
<!-- Will users need to update their code or configurations? -->

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
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---------

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

docs/guides/contributing/releasing.md

@@ -10,7 +10,7 @@
 
 The release workflow will automatically:
 - Build binaries for 6 platforms (Linux, macOS, Windows × amd64, arm64)
-- Create and push Docker images with `:latest` and `:vX.Y.Z` tags
+- Create and push Docker images with `:latest` and `:X.Y.Z` tags (note: no 'v' prefix)
 - Attach all artifacts to the GitHub release
 - Generate checksums and signatures
 
@@ -18,12 +18,12 @@ The release workflow will automatically:
 
 - Docker images will be available at:
   - `ghcr.io/modelcontextprotocol/registry:latest` - Latest stable release
-  - `ghcr.io/modelcontextprotocol/registry:vX.Y.Z` - Specific release version
+  - `ghcr.io/modelcontextprotocol/registry:X.Y.Z` - Specific release version (note: no 'v' prefix)
 - Binaries can be downloaded from the GitHub release page
 
 **Note:** Releases do not automatically deploy to production. To deploy a release to production:
 
-1. Update `mcp-registry:imageTag` in `deploy/Pulumi.gcpProd.yaml` to the desired version (e.g., `v1.2.3`)
+1. Update `mcp-registry:imageTag` in `deploy/Pulumi.gcpProd.yaml` to the desired version (e.g., `1.2.3` - note: no 'v' prefix)
 2. Commit and push the change to the `main` branch
 3. The [deploy-production.yml](../../../.github/workflows/deploy-production.yml) workflow will automatically trigger and deploy the specified version
 
@@ -34,10 +34,12 @@ See the [deployment documentation](../../../deploy/README.md) for more details.
 The registry publishes different Docker image tags for different use cases:
 
 - **`:latest`** - Latest stable release (updated only on releases)
-- **`:vX.Y.Z`** - Specific release versions (e.g., `:v1.0.0`)
+- **`:X.Y.Z`** - Specific release versions (e.g., `:1.0.0` - note: no 'v' prefix)
 - **`:main`** - Rolling tag updated on every push to main branch (continuous deployment)
 - **`:main-YYYYMMDD-sha`** - Specific development builds from main branch
 
+**Note:** Git release tags include the 'v' prefix (e.g., `v1.0.0`), but Docker image tags follow the standard Docker convention and do not include the 'v' prefix (e.g., `1.0.0`).
+
 ## Versioning
 
 We use semantic versioning (SemVer):