fix: Add upgrade doc and fix variable description #339

Job	Run time
Collect workflow inputs	3s
Max TF pre-commit	1m 33s
Min TF pre-commit (.)	19s
Min TF pre-commit (./examples/s3-import-mysql)	27s
Min TF pre-commit (./examples/blue-green-deployment)	21s
Min TF pre-commit (./examples/enhanced-monitoring)	33s
Min TF pre-commit (./examples/cross-region-replica-postgres)	23s
Min TF pre-commit (./examples/replica-mysql)	21s
Min TF pre-commit (./examples/replica-postgres)	33s
Min TF pre-commit (./examples/complete-mysql)	23s
Min TF pre-commit (./examples/groups)	20s
Min TF pre-commit (./examples/complete-oracle)	25s
Min TF pre-commit (./examples/role-association-postgres)	32s
Min TF pre-commit (./examples/complete-mssql)	23s
Min TF pre-commit (./examples/complete-postgres)	19s
Min TF pre-commit (./modules/db_subnet_group)	22s
Min TF pre-commit (./modules/db_instance)	18s
Min TF pre-commit (./modules/db_instance_role_association)	24s
Min TF pre-commit (./modules/db_instance_automated_backups_replication)	27s
Min TF pre-commit (./modules/db_option_group)	32s
Min TF pre-commit (./modules/db_parameter_group)	24s
	9m 22s

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