Added CI tests for MySQL 9.x

close #303

Added CI tests for MySQL 9.x

close #303

caching_sha2_password can now be used without TLS

Fixed a problem that caused pfr_by_name<T> to fail compilation when T has no fields under older clang/libc++ versions.

close #313
close #483

Fixed a race condition in per-operation cancellation in variant_stream

close #454

Fixed a race condition in per-operation cancellation in variant_stream

close #454

Improved discussion and examples

Added a tutorial on UPDATEs, transactions and multi-queries
Added a tutorial on connection_pool
Added a tutorial on error handling
Added examples on INSERTs and DELETEs
Rewrote the discussion page on character sets
Added a discussion page on the templated connection class
Removed superseded examples on timeouts and multi-queries
Updated the coverage build to gcc-14 (gcc-13 was using a non-LTS release
that caused problems)

Contributes to #365 and #366

Boost 1.87: new discussion and examples (part 1)

Added tutorials 2, 3 and 4
Changed most of the discussion to use any_connection
Added examples on disabling TLS, multi-function operations, multi-queries and transactions
All examples now use any_connection
Automate parts of example qbk generation

Partially addresses #365 and #366

Boost 1.86 new CI builds

Added gcc-14 build
Updated mysql8 to MySQL 8.4.1
Updated mariadb to MariaDB 11.4.2
Updated some CMake builds to the latest compiler versions
Updated GHA workflows to use Node 20 actions
Updated deprecated ENV commands in Dockerfiles
Removed debugging statements in OSX CI build
DB entrypoints are now inline scripts in Dockerfiles
TSAN is now run in ARM CIs and recent gcc's
TSAN is now disabled for TS executors

close #302

Boost 1.86 new CI builds

Added gcc-14 build
Updated mysql8 to MySQL 8.4.1
Updated mariadb to MariaDB 11.4.2
Updated some CMake builds to the latest compiler versions
Updated GHA workflows to use Node 20 actions
Updated deprecated ENV commands in Dockerfiles
Removed debugging statements in OSX CI build
DB entrypoints are now inline scripts in Dockerfiles
TSAN is now run in ARM CIs and recent gcc's
TSAN is now disabled for TS executors

close #302

Preventively disabled -Werror in CMake tests

This is recommended because some users build tests as part of their builds. See #183