x/tools/gopls: add instrumentation to gopls MCP server calls

[ethanalee-work]

Objectives

There is a need to add instrumentation to the gopls MCP server to understand usage patterns of different MCP tools. Stretch goal to add bucketing for vulnerabilities that are exposed via gopls.vulncheck.

[gopherbot]

Change https://go.dev/cl/703495 mentions this issue: internal/mcp: add vuln counter to MCP instrumentation

[gopherbot]

Change https://go.dev/cl/703358 mentions this issue: internal/mcp: add telemetry for MCP tool usage