Generate service docs from Go files

[CapacitorSet]

There have been some talks of adding configuration examples in the source files, so I figured I'd make them machine-readable and integrate them with Jekyll.

This PR adds a script that can parse descriptions from service files and output them as a JSON file, which can then be used in Jekyll to generate the documentation files.

Example usage:

$ go run scripts/gen-service-docs.go services > /honeytrap-docs/services.json
Added service redis
$ cat /honeytrap-docs/services.json
[
    {
        "Name": "redis",
        "Description": "The Redis service will simulate a redis server. Currently the INFO command has been implemented.",
        "Config": "version=\"4.0.6\"\nos=\"Linux 4.9.49-moby x86_64\"\n",
        "Filename": "services/redis/redis.go"
    }
]

I added a quick example of the metadata in redis.go; it shouldn't take much to do the same for all services.

[codecov-io]

Codecov Report

Merging #390 into master will increase coverage by 0.45%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #390      +/-   ##
==========================================
+ Coverage   41.22%   41.67%   +0.45%     
==========================================
  Files          81       78       -3     
  Lines        8949     8796     -153     
==========================================
- Hits         3689     3666      -23     
+ Misses       4828     4705     -123     
+ Partials      432      425       -7

Impacted Files	Coverage Δ
server/honeytrap.go	3.15% <0%> (-0.29%)	⬇️
server/matchers.go	0% <0%> (ø)	⬆️
services/ldap/search.go	0% <0%> (ø)	⬆️
services/smtp/storage.go	65.15% <0%> (ø)	⬆️
services/limiter.go	0% <0%> (ø)	⬆️
server/options.go	0% <0%> (ø)	⬆️
services/ldap/bind.go	47.5% <0%> (ø)	⬆️
services/copy.go	0% <0%> (ø)	⬆️
pushers/elasticsearch/elasticsearch.go	0% <0%> (ø)	⬆️
pushers/splunk/config.go	0% <0%> (ø)	⬆️
... and 60 more

---

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[nl5887]

Great idea. In hindsight, this docs can be generated out of the config struct within the service configuration itself. If we add comment to there, we can reuse them in the generated docs.

[CapacitorSet]

I'll try that and push a commit later today.

[CapacitorSet]

Done.

It now expects a struct whose name ends in Config, and for which members that have a toml tag also have a default tag.

In code, it expects this:

type redisServiceConfig struct {
	Version string `toml:"version" default:"4.0.6"`
	Os string `toml:"os" default:"Linux 4.9.49-moby x86_64"`
}

And produces this:

os = "Linux 4.9.49-moby x86_64"
version = "4.0.6"