fix(contrib): migrate legacy ToolServer and MCPServer manifests to v1alpha3 RemoteMCPServer

[mohit-bhandari45]

Summary

Fixes #2819.

Four example manifests and Helm templates under contrib/tools/ declared legacy kagent.dev/v1alpha1 ToolServer and MCPServer resources, which were deleted in prior API refactors (#2686 and #822). kubectl apply on these files failed with no matches for kind.

This PR migrates all contrib/tools/ manifests, Helm chart templates, and unit tests to the active kagent.dev/v1alpha3 RemoteMCPServer specification.

Changes Made

• contrib/tools/context7.mcp.yaml: Migrated kagent.dev/v1alpha1 ToolServer to kagent.dev/v1alpha3 RemoteMCPServer.
• contrib/tools/mcpserver-custom-registry-example.yaml: Migrated kagent.dev/v1alpha1 MCPServer to kagent.dev/v1alpha3 RemoteMCPServer.
• contrib/tools/github-mcp-server/templates/toolserver.yaml: Migrated Helm template to kagent.dev/v1alpha3 RemoteMCPServer, moving connection fields (url, protocol, timeout, headersFrom) to top-level spec:, and updating ValueSource keys (name instead of valueRef).
• contrib/tools/mcp-grafana/templates/toolserver.yaml: Migrated Helm template to kagent.dev/v1alpha3 RemoteMCPServer with top-level spec.url and spec.timeout.
• contrib/tools/mcp-grafana/tests/toolserver_test.yaml: Updated Helm unit test assertions to match isKind: RemoteMCPServer and updated spec paths.

Verification

Verified modified standalone manifests against a Kubernetes cluster with Kagent CRDs installed:

kubectl apply --dry-run=client -f contrib/tools/context7.mcp.yaml
# remotemcpserver.kagent.dev/context7-mcp created (dry run)

kubectl apply --dry-run=client -f contrib/tools/mcpserver-custom-registry-example.yaml
# remotemcpserver.kagent.dev/example-custom-registry created (dry run)