Add HTTP status pages

[lukedirtwalker]

The HTTP pages are exposed via the existing monitoring port.

1. Add config page to all SCION services (content of the toml config)
2. Add info page to all SCION services (just the build version at the moment)
3. Add topology page to all SCION services (content of loaded topology)

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This change is 

[sustrik]

Reviewed 10 of 10 files at r1, 1 of 3 files at r2.
Reviewable status: 9 of 11 files reviewed, 4 unresolved discussions (waiting on @lukedirtwalker and @sustrik)

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go/border/brconf/BUILD.bazel, line 27 at r2 (raw file):

    name = "go_default_test",
    srcs = ["params_test.go"],
    data = glob(["testdata/**"]),

Why is this needed?

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go/cert_srv/main.go, line 186 at r1 (raw file):

	http.HandleFunc("/info", env.InfoHandler)
	http.HandleFunc("/topology", itopo.TopologyHandler)
	cfg.Metrics.StartPrometheus()

Was it the case that prom server was not running at all in CS?

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go/path_srv/main.go, line 324 at r1 (raw file):

	var buf bytes.Buffer
	toml.NewEncoder(&buf).Encode(cfg)
	fmt.Fprint(w, buf.String())

Missing newline

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go/sciond/main.go, line 300 at r1 (raw file):

	var buf bytes.Buffer
	toml.NewEncoder(&buf).Encode(cfg)
	fmt.Fprint(w, buf.String())

Missing newline

[lukedirtwalker]

Reviewable status: 9 of 11 files reviewed, 4 unresolved discussions (waiting on @sustrik)

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go/border/brconf/BUILD.bazel, line 27 at r2 (raw file):

Previously, sustrik (Martin Sustrik) wrote…

Why is this needed?

I just ran make gazelle and this was added

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go/cert_srv/main.go, line 186 at r1 (raw file):

Previously, sustrik (Martin Sustrik) wrote…

Was it the case that prom server was not running at all in CS?

Yes just checked on master, CS doesn't export metrics. Maybe it got lost during a refactoring.

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go/path_srv/main.go, line 324 at r1 (raw file):

Previously, sustrik (Martin Sustrik) wrote…

Missing newline

Done.

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go/sciond/main.go, line 300 at r1 (raw file):

Previously, sustrik (Martin Sustrik) wrote…

Missing newline

Done.

[sustrik]

Reviewed 2 of 3 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved