Windows support (agent)

[kolesnikovae]

This PR is the first step toward full-fledged Windows support. With this change, pyroscope can be run on Windows in agent, exec and connect modes.

Limitations:

• Minimal supported version: Windows 10 Build 17063.
• Only gospy and dotnetspy can be used. In contrast to Linux/macOS, on Windows, dotnetspy accounts time spent in unmanaged code.

[codecov]

Codecov Report

Merging #212 (b430e0e) into main (2cc5f0e) will decrease coverage by 0.63%.
The diff coverage is 39.24%.

❗ Current head b430e0e differs from pull request most recent head 985a599. Consider uploading reports for the commit 985a599 to get more accurate results

@@            Coverage Diff             @@
##             main     #212      +/-   ##
==========================================
- Coverage   56.07%   55.45%   -0.62%     
==========================================
  Files          74       82       +8     
  Lines        3089     3214     +125     
==========================================
+ Hits         1732     1782      +50     
- Misses       1186     1252      +66     
- Partials      171      180       +9     

Impacted Files	Coverage Δ
cmd/pyroscope/logging.go	66.67% <0.00%> (-33.33%)	⬇️
cmd/pyroscope/main.go	0.00% <0.00%> (ø)
cmd/pyroscope/main_unix.go	0.00% <0.00%> (ø)
pkg/agent/target/service.go	0.00% <0.00%> (ø)
pkg/agent/target/service_unix.go	0.00% <0.00%> (ø)
pkg/cli/agent_unix.go	0.00% <0.00%> (ø)
pkg/cli/server_unix.go	0.00% <0.00%> (ø)
pkg/cli/usage.go	10.26% <ø> (ø)
pkg/exec/cli_linux.go	13.34% <ø> (ø)
pkg/util/disk/usage_unix.go	60.00% <ø> (ø)
... and 23 more

---

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[kolesnikovae]

FreeSpace on Linux/macOS relies on statfs bfree (free blocks in filesystem), consider use of bavail (free blocks available to unprivileged user).

[petethepig]

LGTM