Update Renovate configuration

[martincostello]

Changes

• Move to .github.
• Use various built-in presets.
• Match labels to dependabot.
• Add custom manager to update OATS in .sh and .ps1 files.

Merge requirement checklist

• Unit tests added/updated
• CHANGELOG.md file updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[Copilot]

Pull Request Overview

This PR relocates the Renovate configuration to the .github directory, adopts a set of built-in presets, and refines labeling and custom manager rules.

• Moved renovate.json from the repository root into .github/renovate.json and removed the old file.
• Updated extends presets (config:best-practices, vulnerability alerts, sign-off, etc.) and aligned labels with Dependabot conventions.
• Added a custom regex manager to update _VERSION variables in PowerShell and shell scripts, and refined packageRules for Docker, GitHub Actions, and NuGet.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
renovate.json	Removed legacy Renovate config from the repository root.
.github/renovate.json	Added new Renovate config: built-in presets, custom managers, labels, and packageRules.

Comments suppressed due to low confidence (3)

.github/renovate.json:22

• [nitpick] The configuration no longer includes a manager placeholder label ({{{manager}}}), which could reduce PR visibility by manager type. Consider re-adding "{{{manager}}}" to ensure updates remain categorized per manager.

"labels": ["dependencies"]

.github/renovate.json:36

• [nitpick] The label .NET mixes punctuation and casing; consider using a consistent lowercase label such as dotnet to align with other labels (docker, github_actions).

"addLabels": [".NET"]

.github/renovate.json:56

• The vulnerabilityAlerts block expects a labels field rather than addLabels. Using labels will correctly apply the security label to vulnerability PRs.

"addLabels": ["security"]