[go-experimental] Fix multiple go compilation errors and enable go integration test

Created by: sebastien-rosset

Fix issues listed in #5074 (closed)

The generated go-experimental code has multiple issues that cause syntax errors:

Use but does not define the "NullableMap" type Refer to the "NullableTime.Time" type, but the type is actually "NullableTime" Import but does not use the "time" package Refer to the Nullable[]map[string]interface{}, which is not a valid golang type. Some "const" values are defined twice with the same identifier, once for the enum value, and once for the default value. Other issues found:

Missing pom.xml files in the go and go-experimental directories.

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