rds.DBInstance - fix "up to date" when using ApplyImmediately

[chlunde]

Description of your changes

DBInstance is in the example is never "up to date"

	2022/03/09 22:26:23   &v1alpha1.DBInstanceParameters{
		... // 4 ignored and 40 identical fields
		TDECredentialPassword: nil,
		Timezone:              nil,
		CustomDBInstanceParameters: v1alpha1.CustomDBInstanceParameters{
			... // 14 ignored and 2 identical fields
	- 		ApplyImmediately: nil,
	+ 		ApplyImmediately: &true,
		},
	  }

	2022-03-09T22:26:24.297+0100	DEBUG	provider-aws	Successfully requested update of external resource

ApplyImmediately is not an observable field, but an option for the modify API call,
so we should not compare it.

With the fix:

	2022-03-09T22:31:55.197+0100	DEBUG	provider-aws	External resource is up to date	{"controller": "managed/dbinstance.rds.aws.crossplane.io", "request": "/example-dbinstance", "uid": "b097b3ca-f29a-44e4-8cb4-1d4488a711c6", "version": "940953", "external-name": "example-dbinstance", "requeue-after": "2022-03-09T22:32:55.197+0100"}

I have:

• Read and followed Crossplane's [contribution process].
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

Apply example file and check logs.

Added temporary debugging (not in commit):

diff --git a/pkg/controller/rds/dbinstance/setup.go b/pkg/controller/rds/dbinstance/setup.go
index 4f22ac8b..b8317a72 100644
--- a/pkg/controller/rds/dbinstance/setup.go
+++ b/pkg/controller/rds/dbinstance/setup.go
@@ -3,6 +3,7 @@ package dbinstance
 import (
        "context"
        "encoding/json"
+       "log"
        "strconv"
        "strings"
        "time"
@@ -329,7 +330,7 @@ func (e *custom) isUpToDate(cr *svcapitypes.DBInstance, out *svcsdk.DescribeDBIn
                return false, err
        }
 
-       return cmp.Equal(&svcapitypes.DBInstanceParameters{}, patch, cmpopts.EquateEmpty(),
+       diff := cmp.Diff(&svcapitypes.DBInstanceParameters{}, patch, cmpopts.EquateEmpty(),
                cmpopts.IgnoreTypes(&xpv1.Reference{}, &xpv1.Selector{}, []xpv1.Reference{}),
                cmpopts.IgnoreFields(svcapitypes.DBInstanceParameters{}, "Region"),
                cmpopts.IgnoreFields(svcapitypes.DBInstanceParameters{}, "Tags"),
@@ -340,7 +341,9 @@ func (e *custom) isUpToDate(cr *svcapitypes.DBInstance, out *svcsdk.DescribeDBIn
                cmpopts.IgnoreFields(svcapitypes.DBInstanceParameters{}, "PreferredMaintenanceWindow"),
                cmpopts.IgnoreFields(svcapitypes.DBInstanceParameters{}, "PreferredBackupWindow"),
                cmpopts.IgnoreFields(svcapitypes.CustomDBInstanceParameters{}, "ApplyImmediately"),
-       ) && !maintenanceWindowChanged && !backupWindowChanged && !pwChanged, nil
+       )
+       log.Println(diff)
+       return diff == "" && !maintenanceWindowChanged && !backupWindowChanged && !pwChanged, nil
 }
 
 func createPatch(out *svcsdk.DescribeDBInstancesOutput, target *svcapitypes.DBInstanceParameters) (*svcapitypes.DBInstanceParameters, error) {