feat(sumologicschemaprocessor): add squashing single values in nesting processor

[aboguszewski-sumo]

Updates #865

This PR adds a feature to nesting processor that squashes maps that have only one key-value pair. For example:

{
"k8s": {
  "pods": {
    "a" : "A",
    "b": "B"
    }
  }
}

gets squashed into

{
"k8s.pods": {
    "a" : "A",
    "b": "B"
    }
}

This feature is disabled by default.

Two things to note:

• Perhaps this implementation contains too much map copying, but I wanted to finish this before Christmas and eventually fix later.
• I tried to create an algorithm that does this while doing the initial nesting, but I found it to be too complex and not necessarily faster.

[sumo-drosiek]

🤷