Move joinGet into StorageJoin

Protect JoinSource with lock, add test

Add comments about locking logic

Do only merging of sorted blocks on initiator with distributed_group_by_no_merge=2

Improve backtrace catching on server failures in CI for fast-tests

Compression for Memory tables

Increase buffer for uncaught exception / std::terminate

DOCSUP-5974: documented decodeXMLComponent function

Check for EINTR in epoll_wait

Use PIPE_BUF over some magic number 1024 in terminate_handler, since
according to pipe(7):

    PIPE_BUF
           POSIX.1  says  that  write(2)s of less than PIPE_BUF bytes must be atomic

Also note that 1024, is too small, especially for C++ stacktraces (and
especially for debug builds, that contains lots of non-inlined helpers
for various ptrs).

Adding documentation on how to use LDAP server as external user authenticator or directory

rabbitmq: add missing format factory settings

Fix usage of 'distinct' combinator with 'state' combinator

Fix COM_FIELD_LIST response in MySQL protocol

Improve backtrace catching on server failures in CI for stress tests

Fix push to dockerhub

* Refactoring: part 1

* Refactoring: part 2

* Handle request using ReadBuffer interface

* Struggles with ReadBuffer's

* Fix URI parsing

* Implement parsing of multipart/form-data

* Check HTTP_LENGTH_REQUIRED before eof() or will hang

* Fix HTTPChunkedReadBuffer

* Fix build and style

* Fix test

* Resist double-eof

* Fix arcadian build

Rename untyped function reinterpretAs into reinterpret

ccache 4.2+ does not requires any quirks for SOURCE_DATE_EPOCH

https://clickhouse-test-reports.s3.yandex.net/20882/af660140c320ca45bca0edfd89000b3c6da8ee6a/functional_stateless_tests_flaky_check_(address).html#fail1

And besides "ccache <some ccache options> compiler" does not work, since
it interpret everything as ccache options.

Refs: https://github.com/ccache/ccache/commit/cad2416291c042443cf0c045047c34a2e07e103a

When distributed_group_by_no_merge=2 is used (or when
optimize_distributed_group_by_sharding_key takes place), remote servers
will do full ORDER BY, so initiator can skip this step and do only merge
of ordered blocks.

Regardless
distributed_group_by_no_merge=2/optimize_distributed_group_by_sharding_key