feat: Add release deployment template

[lourens-octopus]

Add function to retrieve the release deployment template for a specific release

[sc-122277]

[Copilot]

Pull Request Overview

This PR adds functionality to retrieve release deployment templates from the Octopus Deploy API. It introduces a new API endpoint and service method to fetch deployment template information for a specific release.

• Adds new URI template constant for the release deployment template endpoint
• Implements GetReleaseDeploymentTemplate function with proper parameter validation
• Defines ReleaseDeploymentTemplate and DeploymentPromotionTarget data structures

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
uritemplates/links.go	Adds new URI template constant for release deployment template endpoint
pkg/releases/release_service.go	Implements new service function to retrieve release deployment templates
pkg/releases/release_deployment_template.go	Defines data structures for release deployment template response

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