Added a system information HTTP service

[Daniel-WWU-IT]

The new service exposes system information via an HTTP endpoint. This currently only includes Reva version information (which isn't working atm in Reva's build system as it seems). The information are exposed in the form of Prometheus metrics so that we will be able to gather these in a streamlined way with some Mentix extensions yet to come.

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[labkode]

Very nice job and sorry for late review.

#1060

[ishank011]

Can we use the same exporter as we do for the prometheus HTTP service? That is a lot cleaner and since both of them are running similar services, it would be better to have them use the same packages.

@labkode @Daniel-WWU-IT

[Daniel-WWU-IT]

@ishank011 Are you referring to using the contrib.go.opencensus.io/exporter/prometheus package? No, I don't think so, as that package is just using the official Go client library (as I do) to expose its own metrics. It is not a library that can be used to expose custom metrics I believe, though I'm not entirely sure if you can't add custom metrics there as well. As said, it also uses the same Go library internally as I do.

Or are you referring to merging the two services and include the system info in the "main" metrics exported by Reva? I suppose that is possible, but it still would require using the Prometheus Go library directly anyway.

[labkode]

@ishank011 that is a very good point. I keep track of it here: #1070
I'll add it to the new sprint.