refactor: extract PR body template from update-dependencies workflow

[Copilot]

Addresses feedback to extract hardcoded PR body content from the update-dependencies.yml workflow into a reusable template file for improved maintainability.

Changes

• Created .github/VSCODE_EXTENSION_UPDATE_PR_TEMPLATE.md containing the VS Code extension update notice
• Updated workflow to use cat to read template instead of inline echo commands

Before:

- run: |
    {
      echo "> [!NOTE]"
      echo "> Before merging this PR, please conduct a manual test..."
      echo ""
      echo "${{ steps.update-extensions.outputs.markdown-summary }}"
    } >> pull-request-body.md

After:

- run: |
    {
      cat .github/VSCODE_EXTENSION_UPDATE_PR_TEMPLATE.md
      echo "${{ steps.update-extensions.outputs.markdown-summary }}"
    } >> pull-request-body.md

This follows the existing pattern of template files in .github/ (e.g., PULL_REQUEST_TEMPLATE.md, RELEASE_TEMPLATE.md) and makes the notice message easier to update.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Pull Request Report (#1119)

Static measures

Description	Value
Number of added lines	4
Number of deleted lines	3
Number of changed files	2
Number of commits	2
Number of reviews	0
Number of comments (w/o review comments)	1
Number of reviews that contains a comment to resolve	0
Number of reviews that requested a change from the author	0
Number of reviews that approved the Pull Request	0
Get the total number of participants of a Pull Request	3

Time related measures

Description	Value
PR lead time (from creation to close of PR)	11.2 Min
Time that was spend on the branch before the PR was created	0 Sec
Time that was spend on the branch before the PR was merged	0 Sec
Time to merge after last review	0 Sec

Status check related measures

Description	Value
Total runtime for last status check run (Workflow for PR)	32 Sec
Total time spend in last status check run on PR	33 Sec