Add docs for our bc promise and our versioning #4156

Job	Run time
mariadb (locked, 8.3, ubuntu-latest, 10.5)	1m 20s
mysql (locked, 8.3, ubuntu-latest, 5.7)	1m 26s
mariadb (locked, 8.3, ubuntu-latest, 10.6)	50s
mysql (locked, 8.3, ubuntu-latest, 8.0)	1m 26s
mariadb (locked, 8.3, ubuntu-latest, 10.11)	55s
Sqlite (locked, 8.3, ubuntu-latest)	13s
Postgres (locked, 8.3, ubuntu-latest, 12.20)	1m 26s
mysql (locked, 8.3, ubuntu-latest, 8.4)	59s
mariadb (locked, 8.3, ubuntu-latest, 11.1)	50s
Postgres (locked, 8.3, ubuntu-latest, 13.16)	57s
mysql (locked, 8.3, ubuntu-latest, 9.0)	56s
mariadb (locked, 8.3, ubuntu-latest, 11.4)	1m 27s
Postgres (locked, 8.3, ubuntu-latest, 14.13)	1m 24s
Postgres (locked, 8.3, ubuntu-latest, 15.8)	58s
Postgres (locked, 8.3, ubuntu-latest, 16.4)	1m 25s
Postgres (locked, 8.3, ubuntu-latest, 17.0)	1m 24s
	17m 56s

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