[WIP] Add support for multiple PR templates selection

[Copilot]

• Add githubPullRequests.createFromTemplate setting to package.json with values: none, first, prompt
• Add localization strings for the new setting in package.nls.json
• Add the setting constant to src/common/settingKeys.ts
• Update folderRepositoryManager.ts to support fetching all templates instead of just the first one
• Update createPRViewProvider.ts to handle template selection based on the new setting
• Add logic to prompt user when prompt option is selected and multiple templates exist
• Test the implementation with a repository that has multiple PR templates
• Add or update tests if needed

Original prompt

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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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