feat: Added GroupedRelation empty filter

[rlcc885]

(cherry picked from commit f01088d8a53aca6496051120f02ce0acdfb9e67a)

[Blackdread]

Hi, what was it for exactly?

[rlcc885]

Hi, nice to meet you, when you select the option to group export-file-structure-type: GROUPED_RELATIONS_SEPARATE_VIEWS one-to-one or one-to-many relationships, but they do not exist as such in the schema, empty structures are generated. For example:

relationship ManyToOne {
}
relationship OneToOne {
}

The commit tries to solve it

[Blackdread]

Alright.
Why did you decide to close your PR ?

After, the fact that empty ones are generated, I do not mind it, it makes it clear that none were seen/found by the code logic.

[rlcc885]

Of course, at the programming level there is no problem, but when using the web version of the jdl editor, it marks an error when generating the relationship structure as empty. The focus of the commit was aiming at web integration.
Regarding the reason for closing the PR, it is because I made a missclick to the fork of my account, but I could generate a new one.