Add http file showcasing how to use the management API

No public client for now since it deviates from the gRPC protocol for everything else. Perhaps we'll introduce a typed API at some point?

Author: kzu

src/xAI.Tests/.gitignore

@@ -0,0 +1 @@
+http-client.env.json

src/xAI.Tests/management.http

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+### List API keys
+GET https://management-api.x.ai/auth/teams/{{teamId}}/api-keys
+Authorization: Bearer {{token}}
+
+### List ACL values
+GET https://management-api.x.ai/auth/teams/{{teamId}}/endpoints
+Authorization: Bearer {{token}}
+
+### List models
+GET https://management-api.x.ai/auth/teams/{{teamId}}/models
+Authorization: Bearer {{token}}
+
+### Validate management key
+GET https://management-api.x.ai/auth/management-keys/validation
+Authorization: Bearer {{token}}
+
+### Create API key
+POST https://management-api.x.ai/auth/teams/{{teamId}}/api-keys
+Authorization: Bearer {{token}}
+
+  {
+    "name": "kzu-user",
+    "acls": [
+      "api-key:endpoint:*",
+      "api-key:model:*"
+    ]
+  }
+
+### Check API Key
+GET https://management-api.x.ai/auth/api-keys/{{userKeyId}}/propagation
+Authorization: Bearer {{token}}