Fix broken links by adding Azure Static Web Apps redirects (#2772)

This PR addresses broken links that result in 404 errors due to the
documentation site migration from
`https://nkdagility.com/learn/azure-devops-migration-tools` to
`https://devopsmigration.io/`.

## Changes Made

Added two redirect rules to `docs/staticwebapp.config.json`:

1. **Remove old path prefix**: Redirects
`/learn/azure-devops-migration-tools/*` to `/*`
- Example:
`https://devopsmigration.io/learn/azure-devops-migration-tools/Reference/FieldMaps/FieldValueMap/`
→ `https://devopsmigration.io/Reference/FieldMaps/FieldValueMap/`
- This affects approximately 70 pages (all FieldMaps, Processors,
Endpoints, etc.)

2. **Remove .md extension**: Redirects `*/index.md` to `*/`
- Example:
`https://devopsmigration.io/Reference/Processors/Endpoints/index.md` →
`https://devopsmigration.io/Reference/Processors/Endpoints/`

## Configuration

```json
{
  "routes": [
    {
      "route": "/learn/azure-devops-migration-tools/*",
      "redirect": "/{*}"
    },
    {
      "route": "*/index.md",
      "redirect": "{*}/"
    }
  ],
  "responseOverrides": {
    "404": {
      "rewrite": "/404"
    }
  }
}
```

These redirect rules follow the Azure Static Web Apps configuration
format and will automatically handle the broken links when deployed.

Fixes #2771.

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Author: MrHinsh

docs/staticwebapp.config.json

@@ -1,4 +1,14 @@
 {
+  "routes": [
+    {
+      "route": "/learn/azure-devops-migration-tools/*",
+      "redirect": "/{*}"
+    },
+    {
+      "route": "*/index.md",
+      "redirect": "{*}/"
+    }
+  ],
   "responseOverrides": {
     "404": {
       "rewrite": "/404"