mcp: add mcp method and tool logging to authorize (#5668)

## Summary

Adds support for extending authorization log with Model Context Protocol
details.

i.e. 
```json
{
  "level": "info",
  "server-name": "all",
  "service": "authorize",
  "mcp-method": "tools/call",
  "mcp-tool": "describe_table",
  "mcp-tool-parameters": { "table_name": "Categories" },
  "allow": true,
  "allow-why-true": ["email-ok", "mcp-tool-ok"],
  "deny": false,
  "deny-why-false": [],
  "time": "2025-06-24T17:40:41-04:00",
  "message": "authorize check"
}
```

## Related issues

Fixes
https://linear.app/pomerium/issue/ENG-2393/mcp-authorize-each-incoming-request-to-an-mcp-route

## User Explanation

<!-- How would you explain this change to the user? If this
change doesn't create any user-facing changes, you can leave
this blank. If filled out, add the `docs` label -->

## Checklist

- [x] reference any related issues
- [x] updated unit tests
- [x] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [x] ready for review

authorize/log.go

@@ -184,6 +184,21 @@ func populateLogEvent(
 		return evt
 	case log.AuthorizeLogFieldIP:
 		return evt.Str(string(field), req.HTTP.IP)
+	case log.AuthorizeLogFieldMCPMethod:
+		if method := req.MCP.Method; method != "" {
+			return evt.Str(string(field), req.MCP.Method)
+		}
+		return evt
+	case log.AuthorizeLogFieldMCPTool:
+		if req.MCP.ToolCall != nil {
+			return evt.Str(string(field), req.MCP.ToolCall.Name)
+		}
+		return evt
+	case log.AuthorizeLogFieldMCPToolParameters:
+		if req.MCP.ToolCall != nil && req.MCP.ToolCall.Arguments != nil {
+			return evt.Interface(string(field), req.MCP.ToolCall.Arguments)
+		}
+		return evt
 	case log.AuthorizeLogFieldMethod:
 		return evt.Str(string(field), req.HTTP.Method)
 	case log.AuthorizeLogFieldPath: