Add documentation related to tradeoff and performance

[kostacasa]

Would be useful to understand how gatewayD behaves compared to various runtime modes of pgBouncer. Are there any impacts to transactionality, prepared statements etc?

It would also be useful to indicate some supported/recommended configurations in terms of concurrent connection capacity/pooling across standard AWS/GCP/Azure VM sizes.

[mostafa]

Hey @kostacasa,

We have plans to do this test and there are already tickets for it:

• Write k6 tests for various parts of the system gatewayd#188

Also I've done some small benchmarks using pgbench and psql timing and the results are published here.

I'd be happy to know if there are any benchmarks I can use as a baseline to test against.