Guardrails: validate guardrails Secret and add config types

[maleck13]

Summary

Add guardrails Secret validation and config type scaffolding (Part 1 of guardrails feature).

• Guardrails/external/NeMo Secret schema and validation
• Wire validation into MCPGatewayExtension reconciler via mcp.kuadrant.io/guardrails-ref annotation
• Config propagation types (GuardrailsConfig, MCPServer.GuardrailsConfigIDs, BrokerConfig.GlobalGuardrailsConfigIDs)
• maxBodyBytes spec field and new status condition reasons

Parent issue: #1302

[david-martin]

Completed by #1370 (merged after v0.9.0). Moving to v1.0 so the milestone matches when this landed. Remaining guardrails work stays on #1301.