Performance documentation

[fabianfett]

[pokryfka]

@fabianfett please let me know if you'd like any X-Ray graphs to be generated.

If possible, I think it would be fair to mention performance of Foundation JSON encoder/decoder per https://github.com/swift-server/swift-aws-lambda-runtime/issues/153

swift-aws-lambda-runtime makes it easy to change it if one knows about it.

For reference results of a cold run of the same function with and without Foundation, note:

• shorter initialization (129 vs 168ms), the packages size is ~3MiB smaller without libFoundation.so which (uncompressed) is 11.8 MiB size; although the heaviest one is libicudataswift.so.65 with 28 MiB (!)
• much faster DecodeIn(11.9 vs 173ms) and EncodeOut(0.1 vs 40.ms)
• lambda handlers use encoders provided by lambda which is probably why the one using Foundation JSONEncoder is slower (can create subsegment for that to check it out); this example decodes and encodes very small payloads, the difference may be bigger if result is bigger
• the difference is much less dramatic for warm runs

[tomerd]

@fabianfett could you please update this PR to be against the main branch so we can delete the old master branch

[tomerd]

closing in inactive PRs, feel free to re-open if still relevant