Oracle, impossible to add feature with an identity field

[SebastienPeillet]

Describe the bug
In Oracle, there is a type of field that generated values as serial type in postgresql. This type is called identity and values are generated by default or always.

It's not possible to add feature with digitize maptool nor table attribute when the identity field is always generated because oracle does not allow a insert request where a value (even the default value with the sequential) is given for this field.

For example in the image above, a table with a pk field (identity generated always) will not allow :

INSERT INTO test( "pk", "cnt", "name", "name2", "num_char", "geom" ) VALUES ( ?, ?, ?, ?, ?, ? )

the request should be :

INSERT INTO test("cnt", "name", "name2", "num_char", "geom") VALUES ( ?, ?, ?, ?, ? )

without the pk field.

Futhermore, default value like "ISEQ$$_75967".nextval (sequential for identity field) is not interpreted with the digitize maptool for both mode :

when the identity value is generated by default and not always, it is possible to customize the value to do it work.

How to Reproduce

1. create a table with a identity field :
   CREATE TABLE QGIS.POINT_DATA_IDENTITY ( "pk" NUMBER GENERATED ALWAYS AS IDENTITY PRIMARY KEY, GEOM SDO_GEOMETRY);
2. add the layer to your qgis project
3. Try to add a new feature with digitize maptool or attribute table
4. It's not possible to commit the result

QGIS and OS versions

QGIS version	3.10.1-A Coruña	QGIS code revision	1d221185e1
Compiled against Qt	5.12.2	Running against Qt	5.12.2
Compiled against GDAL/OGR	2.4.0	Running against GDAL/OGR	2.4.0
Compiled against GEOS	3.7.1-CAPI-1.11.1	Running against GEOS	3.7.1-CAPI-1.11.1 27a5e771
Compiled against SQLite	3.27.2	Running against SQLite	3.27.2
PostgreSQL Client Version	11.5 (Ubuntu 11.5-0ubuntu0.19.04.1)	SpatiaLite Version	4.3.0a
QWT Version	6.1.4	QScintilla2 Version	2.10.4
Compiled against PROJ	5.2.0	Running against PROJ	Rel. 5.2.0, September 15th, 2018
OS Version	Ubuntu 19.04	This copy of QGIS writes debugging output.
Active python plugins	thyrsis

Additional context