x/tools/gopls: add counters for MCP server usage

[findleyr]

In gopls@v0.20.0, we're launching an experimental MCP server to integrate gopls with MCP-powered coding assistance (beyond the default integration already done via LSP by things like Copilot): #73580. We should be sure to add counters for the usage of this new feature, so that we can see adoption.

This issue just tracks the instrumentation of this telemetry, which must be done before the v0.20.0 release. A separate proposal can propose collection.

CC @h9jiang @madelinekalil

[gabyhelp]

Related Issues

• x/tools/gopls: expose an off-by-default MCP server from gopls #73580

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[gopherbot]

Change https://go.dev/cl/683315 mentions this issue: gopls/internal/cmd: implement counters for mcp server

[gopherbot]

Change https://go.dev/cl/683355 mentions this issue: internal/config: update chart config for mcp server counters

[findleyr]

Looks like this is done.