… Storage Autoscaling)

Reference: #9076

Output from acceptance testing (test failures present in master):

```
--- FAIL: TestAccAWSDBInstance_optionGroup (9.60s)
--- PASS: TestAccAWSDBInstance_IsAlreadyBeingDeleted (407.82s)
--- PASS: TestAccAWSDBInstance_kmsKey (447.28s)
--- PASS: TestAccAWSDBInstance_iamAuth (468.51s)
--- PASS: TestAccAWSDBInstance_basic (469.82s)
--- PASS: TestAccAWSDBInstance_generatedName (509.47s)
--- PASS: TestAccAWSDBInstance_namePrefix (509.57s)
--- PASS: TestAccAWSDBInstance_DeletionProtection (534.93s)
--- PASS: TestAccAWSDBInstance_MaxAllocatedStorage (554.00s)
--- PASS: TestAccAWSDBInstance_FinalSnapshotIdentifier_SkipFinalSnapshot (640.05s)
--- FAIL: TestAccAWSDBInstance_ReplicateSourceDb_AutoMinorVersionUpgrade (839.74s)
--- PASS: TestAccAWSDBInstance_subnetGroup (864.75s)
--- PASS: TestAccAWSDBInstance_FinalSnapshotIdentifier (975.11s)
--- FAIL: TestAccAWSDBInstance_S3Import (661.46s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_BackupWindow (1464.99s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_MaxAllocatedStorage (1520.22s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_AvailabilityZone (1536.83s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_IamDatabaseAuthenticationEnabled (1586.30s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_MaintenanceWindow (1635.73s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb (1697.74s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier (1263.54s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_VpcSecurityGroupIds (1349.56s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_BackupRetentionPeriod (1940.63s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_AllocatedStorage (1949.99s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_Port (1519.48s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_AllocatedStorage (1475.69s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_Io1Storage (1389.89s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_Monitoring (1623.10s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_AutoMinorVersionUpgrade (1233.00s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_AvailabilityZone (1245.29s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_ParameterGroupName (1661.06s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_BackupRetentionPeriod (1285.34s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_MultiAZ (2146.49s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_IamDatabaseAuthenticationEnabled (1083.14s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_DeletionProtection (1149.70s)
--- PASS: TestAccAWSDBInstance_portUpdate (570.32s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_BackupWindow (1234.86s)
--- PASS: TestAccAWSDBInstance_enhancedMonitoring (670.62s)
--- PASS: TestAccAWSDBInstance_separate_iops_update (632.53s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_MaintenanceWindow (1335.83s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_Monitoring (1225.51s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_MaxAllocatedStorage (1295.29s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_BackupRetentionPeriod_Unset (1799.33s)
--- PASS: TestAccAWSDBInstance_MinorVersion (343.49s)
--- PASS: TestAccAWSDBInstance_ec2Classic (395.42s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_Port (1173.81s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_VpcSecurityGroupIds_Tags (1094.16s)
--- PASS: TestAccAWSDBInstance_diffSuppressInitialState (443.64s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_Tags (1223.46s)
--- PASS: TestAccAWSDBInstance_cloudwatchLogsExportConfiguration (511.70s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_ParameterGroupName (1284.52s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_VpcSecurityGroupIds (1196.15s)
--- PASS: TestAccAWSDBInstance_EnabledCloudwatchLogsExports_Postgresql (495.06s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_MultiAZ (1638.76s)
--- PASS: TestAccAWSDBInstance_cloudwatchLogsExportConfigurationUpdate (759.27s)
--- PASS: TestAccAWSDBInstance_EnabledCloudwatchLogsExports_Oracle (686.93s)
--- PASS: TestAccAWSDBInstance_MSSQL_TZ (1926.59s)
--- PASS: TestAccAWSDBInstance_MySQL_SnapshotRestoreWithEngineVersion (1864.61s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_PerformanceInsightsEnabled (1527.89s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_PerformanceInsightsEnabled (1632.72s)
--- PASS: TestAccAWSDBInstance_MSSQL_Domain (3296.64s)
--- PASS: TestAccAWSDBInstance_MSSQL_DomainSnapshotRestore (3228.09s)
--- PASS: TestAccAWSDBInstance_SnapshotIdentifier_MultiAZ_SQLServer (4095.19s)
```

… RestoreDBInstancesFromS3 for now

…argument

…e update logic

Reference: #9087 (comment)