Session pool

[CheSema]

https://github.com/ClickHouse/ClickHouse/issues/50217

This PR makes http/https connections reusable for all uses cases.

the main changes here are:

src/Common/HostResolvePool.{h.cpp}

That class resolves host into multiply addresses Features:

• balance address usage. selectBest() chooses the address by random with weights. The more ip is used the lesser weight it has. When new address is happened, it takes more weight. But still not all requests are assigned to the new address.
• join resolve results. In case when host is resolved into different set of addresses, this class join all that addresses and use them. An address expires after history_ time.
• failed address pessimization. If an address marked with setFail() it is marked as faulty. Such address won't be selected until either a) it still occurs in resolve set after history_ time or b) all other addresses are pessimized as well.
• resolve schedule. Addresses are resolved through DB::DNSResolver::instance(). Usually it does not happen more often than once in history_ time. But also new resolve performed each setFail() call.

src/Common/ConnectionPool.{h,cpp}

That classes manage connections to the endpoint Features:

• it uses HostResolvePool for address selecting. See Common/HostResolvePool.h for more info.
• it minimizes number of Session::connect()/Session::reconnect() calls
• stores only connected and ready to use sessions
• connection could be reused even when limits are reached
• soft limit, warn limit, hard limit
• Session::reconnect() uses the pool as well
• comprehensive sensors
• session is reused according its inner state, automatically
• sensors and limits are groped by the logical source of connection: disks, storages, http (the rest).

src/IO/ReadWriteBufferFromHTTP.h

I have removed all unnecessary complications from it. Make more straightforward errors/retries handling.

Changelog category (leave one):

• Not for changelog (changelog entry is not required)

In general It works great. Almost all connections are reused automatically. Even when response is 3xx or 4xx.

[robot-clickhouse]

This is an automated comment for commit 77c5de700f62451c6f2cf55620d9522832b5d56b with description of existing statuses. It's updated for the latest CI running

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[CheSema]

Found a bug: A lot of files are read with default initialized read settings, files like format_version.txt, columns.txt, metadata_version.txt,... and indexes like primary.cidx. By default read settings has http_max_tries = 1, meanwhile if read settings created from default context it would be initializes with http_max_tries = 10. As a quick fix I've made defaults corresponding.

It happens here: https://github.com/ClickHouse/ClickHouse/blob/a1d1f76f67ab29c759374cf5a51b2e1fecf933f8/src/Storages/MergeTree/PartMetadataManagerOrdinary.cpp#L11-L14

[CheSema]

Failed tests https://github.com/ClickHouse/ClickHouse/issues/60625 https://github.com/ClickHouse/ClickHouse/issues/61090