Fix selfRequired: false not making an object-type property optional

[flovouin]

PR Checklist

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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

When using @ApiProperty({ type: 'object', selfRequired: false }) on an object (which is enforced by types, required: false cannot be used on an object as it refers to its own properties), the property is added to the list of required properties. This is a bug.

What is the new behavior?

Setting selfRequired: false on a object-type property does work, and the property is not added to the list of required. This is implemented by having selfRequired taking precedence over required, as selfRequired is non-ambiguous about its intent (it can only be used for object types, with the clear meaning of applying to the decorated property).

Does this PR introduce a breaking change?

• Yes
• No

Other information

Related to #3163.

[kamilmysliwiec]

LGTM