This is a first step to make it accept configuration. Most of the
changes are quite trivial, but I also ran into some difficulties with
query columns and filters. They need the schema for parsing, but parsing
happens before dependencies are instantiated (and even if it was not the
case, parsing is stateless). Therefore, I have added a `Validate()`
method that must be called after instantiation. Various bits `panic()`
if not validated to ensure we catch all cases.
The alternative to make the component manages a global state would have
been simpler but it would break once we add the ability to add or
disable columns.
This is a huge change to make the various subcomponents of the inlet use
the schema to generate the protobuf. For it to make sense, we also
modify the way we parse flows to directly serialize non-essential fields
to Protobuf.
The performance is mostly on par with the previous commit. We are a bit
less efficient because we don't have a fixed structure, but we avoid
loosing too much performance by not relying on reflection and keeping
the production of messages as code. We use less of Goflow2: raw flow
parsing is still done by Goflow2, but we don't use the producer part
anymore. This helps a bit with the performance as we parse less.
Overall, we are 20% than the previous commit and twice faster than the
1.6.4!
```
goos: linux
goarch: amd64
pkg: akvorado/inlet/flow
cpu: AMD Ryzen 5 5600X 6-Core Processor
BenchmarkDecodeEncodeNetflow
BenchmarkDecodeEncodeNetflow/with_encoding
BenchmarkDecodeEncodeNetflow/with_encoding-12 151484 7789 ns/op 8272 B/op 143 allocs/op
BenchmarkDecodeEncodeNetflow/without_encoding
BenchmarkDecodeEncodeNetflow/without_encoding-12 162550 7133 ns/op 8272 B/op 143 allocs/op
BenchmarkDecodeEncodeSflow
BenchmarkDecodeEncodeSflow/with_encoding
BenchmarkDecodeEncodeSflow/with_encoding-12 94844 13193 ns/op 9816 B/op 295 allocs/op
BenchmarkDecodeEncodeSflow/without_encoding
BenchmarkDecodeEncodeSflow/without_encoding-12 92569 12456 ns/op 9816 B/op 295 allocs/op
```
There was a tentative to parse sFlow packets with gopackets, but the
adhoc parser used here is more performant.
But not using it as some linters are either plain incorrect (the one
suggesting to not use nil for `c.t.Context()`) or just
debatable (checking for err value is a good practice, but there are
good reasons to opt out in some cases).
