TypeManager issue: is_changed() returns False when you set an EnumTypeField to a String

# QwikContext
TypeManager issue: is_changed() returns False when you set an EnumTypeField to a String

# Details
```
>>> idrac.config_mgr._sysconfig.BIOS.PxeDev2EnDis = "Enabled"
>>> idrac.config_mgr._sysconfig.BIOS.is_changed()
False
>>> idrac.config_mgr._sysconfig.BIOS.PxeDev2EnDis = TypeHelper.convert_to_enum("Enabled", PxeDev2EnDisTypes)
>>> idrac.config_mgr._sysconfig.BIOS.is_changed()
True
```

# Repro Steps
Run the above code snippet

# Impact
Not able to import the Server Configuration Profile since is_changed returns False.

# NeedBy
Immediately

# Severity
Severity -2 - Medium