Replace MySQL connector option with SMT for mitigating wrong op flag

See DBZ-2775: there, we added a new connector option to have the MySQL connector emit snapshot events with an op of "r" instead of the currently (and incorrectly) emitted "c". To do:

• Change the emitted value to "r" in the code
• Remove that option
• Add an SMT which allows to change "r" back to the old "c" value if needed for migration purposes
• In the release notes highlight the changed default behavior and the removal of the incorrectly added option in 1.4