Move repository structure to Go monorepo

[rogercoll]

As we keep adding code to the package, more dependencies are being added as well. The current packages look independent enough to be used separately in other projects.

See #143 (comment)

[gregkalapos]

Additionally to the fact that packages are fairly independent, I also think those (currently packages) would be naturally better released and versioned independently.

Currently the whole repo is 1 module, so if anything is updated (and needs to be released), then everything has a new version and is released new.

E.g. if a remapper has a new version, we'd push a new version of this whole repo, and users of the enricher, config fetcher, other remappers, and potentially later the attribute package will see the new version, although there is nothing new for those. If there are automated PRs for bumping the version, then those will be also opened for users of those packages. This could be cleaned up by using different modules as well.

[gregkalapos]

Discussed this in the intake services otel weekly. In the meeting there there was no objection.

So far @kruskall raised concerns in #141 (comment) which we'd need to look into.

From my point of view: we can certainly continue with a single module, at this point it does not block us. At the same time, in think most of the packages are in this repo independent and should be released and versioned independently.

#141 will be merged as a package into the single module.

An alternative could be one repo per module, but there was a conclusion it wouldn't really make a significant difference.