feat: add pprof profiling support to interlink, virtual-kubelet, and ssh-tunnel components

[ShantKhatri]

Fixes #400

Summary

This PR adds basic pprof profiling to all three long-running components, interlink, virtual-kubelet, and ssh-tunnel, as a starting point for #400 .

The approach is intentionally simple is as a shared pkg/pprof helper spins up a background HTTP server that exposes Go's standard /debug/pprof/ endpoints. This uses net/http/pprof (the HTTP wrapper around runtime/pprof) which is the lowest-friction way to get profiling working without touching existing server code.

Profiling is off by default. Each component can opt in via:

• A Pprof: block in the YAML config (for interlink and virtual-kubelet)
• CLI flags -pprof, -pprof-port, -pprof-address (for ssh-tunnel)
• Env vars ENABLE_PPROF, PPROF_PORT, PPROF_ADDRESS (all three)

Default ports are 6060 (vk), 6061 (interlink), 6062 (ssh-tunnel) to avoid conflicts when running everything on the same host.

This is intentionally the "easy first step". Down the line we could look at file-based runtime/pprof captures for scheduled/offline profiling, or auth-gating the endpoints for production hardening, but those feel like follow-ups once we've validated the basics work.

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Related issue : #400

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[Copilot]

Pull request overview

This PR introduces basic Go pprof HTTP profiling support across the long-running interLink components (interlink, virtual-kubelet, ssh-tunnel) by adding a shared helper and wiring it into each component with config/flag/env-based enablement.

Changes:

• Added a shared pkg/pprof helper that starts a background net/http/pprof server tied to a context.
• Extended interlink and virtual-kubelet YAML configs with a Pprof block (and added env-var overrides for interlink; env-var overrides are applied in vk main).
• Added CLI flags + env-var overrides to enable/parameterize pprof for ssh-tunnel, plus unit tests for pkg/pprof.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
pkg/virtualkubelet/config.go	Adds PprofConfig and embeds it in the VK config struct for YAML-driven pprof settings.
pkg/pprof/pprof.go	Introduces the shared pprof server starter helper.
pkg/pprof/pprof_test.go	Adds tests to validate pprof server start/disabled behavior.
pkg/interlink/config.go	Adds PprofConfig and supports env-var overrides in interlink config loading.
cmd/virtual-kubelet/main.go	Wires pprof startup into virtual-kubelet with YAML + env-var overrides and default values.
cmd/ssh-tunnel/main.go	Adds pprof CLI flags, env-var overrides, and starts the pprof server.
cmd/interlink/main.go	Starts the pprof server based on loaded config defaults/overrides.

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[ShantKhatri]

Hi @dciangot, changes here are ready for review when you get a chance.

One note: we're suppressing gosec G108 in the pprof import; it's a false positive, since exposing /debug/pprof/ is exactly the intent here. Server defaults to 127.0.0.1, so no external exposure unless explicitly configured.