Add support for multiple PR templates selection

[Copilot]

Adds support for selecting from multiple pull request templates when creating a PR. When a repository has multiple PR templates available, users can now choose which template to use.

Changes Made

• Added templatePrompt option to the existing githubPullRequests.pullRequestDescription setting
• Updated localization strings in package.nls.json for the new option
• Added getAllPullRequestTemplates() method in folderRepositoryManager.ts to fetch all available templates
• Updated createPRViewProvider.ts to show a quick pick selection when templatePrompt is selected and multiple templates exist

Behavior

• template option: Uses the first template found (original behavior, backward compatible)
• templatePrompt option: Shows a quick pick to select from available templates when multiple exist, otherwise uses the first template if only one exists
• Other options (commit, none, Copilot): Continue to work as before

When templatePrompt is selected and multiple templates are available, a quick pick menu displays each template with:

• A label extracted from the first line of the template
• The template length in characters as a description

Testing

• ✅ TypeScript compilation passes
• ✅ Linting and hygiene checks pass
• ✅ Build process completes successfully
• Manual testing with a repository that has multiple PR templates

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Support multiple PR templates</issue_title>
<issue_description>
Type: Feature Request

E.g., the https://github.com/python/peps/ repo has multiple PR templates to choose from depending on the purpose of the PR. It would be nice if a quick pick came up asking which template to use before opening up the UI to fill in the description.

(Apologies if this is a dupe; the issue reporter hit a GH query limit while I was typing in my title.)

Extension version: 0.101.2024110404
VS Code version: Code - Insiders 1.96.0-insider (231d37338a58ff22c223a7ed7d4c1e7142c513d2, 2024-11-04T14:19:41.196Z)
OS version: Windows_NT x64 10.0.26100
Modes:
Remote OS version: Linux x64 5.15.153.1-microsoft-standard-WSL2

<agent_instructions>Add a setting githubPullRequests.createFromTemplate with the values none, first, and prompt. </agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Support multiple PR templates #6454

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[alexr00]

@copilot Actually, we should reuse the setting githubPullRequests.pullRequestDescription. Instead, add a new option to it templatePrompt.

[Copilot]

@copilot Actually, we should reuse the setting githubPullRequests.pullRequestDescription. Instead, add a new option to it templatePrompt.

Updated to add templatePrompt as a new option to the existing githubPullRequests.pullRequestDescription setting instead of creating a separate setting. The template option continues to use the first template (original behavior), while templatePrompt shows a quick pick when multiple templates exist. Changes in commit 7fe6164.