examples: add HTTP feature examples

[Rememorio]

Summary

• Add HTTP client/server examples for standard HTTP service usage.
• Add HTTP RPC and FastHTTP RPC examples with generated public proto stubs.
• Add FastHTTP mux and RESTful mux-filter examples.
• Keep TLS-specific examples out of this PR so they can be reviewed separately.

Tests

• go test ./features/http/... ./features/httprpc/... ./features/fasthttprpc/... ./features/fasthttpmux/... ./features/restful/... -count=1 from examples/
• go test ./... -count=1 from examples/
• git diff --check main...HEAD
• Scanned changed files for internal-only links and local paths

[WineChord]

LGTM