Obfuscation processor and example

[jmacd]

This PR was originally authored by @moh-osman3. With him out of town, I've updated it with several commits in my fork, so this is a replacement PR.

This PR:

• adds Lightstep's generatorreceiver to create synthetic telemetry in a collector pipeline
• adds obfuscation processor that will obfuscate all attributes with string values when recording telemetry

Simple Test

$ cd collector/examples/synthesize
$ go run ../../cmd/otelarrowcol --config ./record.yaml

This writes zstd compressed and obfuscated traces to an output file (e.g cmd/otelarrowcol/recorded_traces.json)

This can be replayed by running

$ cd collector/examples
$ go run ../../cmd/otelarrowcol --config ./replay.yaml

This reads the data in the recorded file and rewrites it in an uncompressed form

You can also read in the compressed file recorded_traces.json with the the benchmark tools e.g.

$ go run ./tools/trace_benchmark --format json collector/cmd/otelarrowcol/recorded_traces.json

(cc @moh-osman3 @lquerel)

[jmacd]

PTAL @lquerel This is working as-is and I found that the obfuscation processor is not obfuscating 100% of fields. With this being less important than unblocking you to try synthetic data, I thought we should merge this. #192

[lquerel]

2 minor comments.
Otherwise, LGTM.

[lquerel]

Yes slices in general as it's possible to have slice of kvlist containing string, or more complex constructs.

[jmacd]

Yes, I'd like to delay until @moh-osman3 returns.

#192

Other fields include metric description and unit, and I suspect there may be more.

[jmacd]

As a possible TODO --
@moh-osman3 I had thrown away the key when obfuscating, to be sure it's not stored and used to de-obfuscate to be even-safer than safe, I guess.