After the main test, run queries from `website.xml` in parallel using
`clickhouse-benchmark`. This can be useful to test the effects of
concurrency on performance. Comparison test can miss some effects
because it always runs queries sequentially, and many of them are even
single-threaded.

This PR adds a server level config for overriding the default max number
of threads in global thread pool that is currently allowed (10,000).

This might be useful in scenarios where there are a large number of
distributed queries that are executing concurrently and where the
default number of max threads might not be necessarily be sufficient.

This adds the `max_thread_pool_size` config to
tests/server-test.xml file.

This adds the docs for the new server level setting
`max_thread_pool_size`.

ISSUES-3985 Support MySQL engine reading Enums type

Add a test for #10102

Fix typos in code

Added a test for #8550

Fix potential FPE.

xeus-clickhouse is a Jupyter kernal for ClickHouse

client exit with unrecognized arguments

…flow-generate-random

Revert "[experiment] maybe fix warnings in integration tests"

…erate-random

Fix array size overflow in generateRandom

…/20.5/12013

…39ce31188edad32d42811a7e2cfd8

Cherry pick #12013 to 20.5: Fix array size overflow in generateRandom