Support variables param in createPipeline

[SamerAdra]

Add support for the optional "variables" parameter in the createPipeline call.
Would be good if this could be implemented as an overload of createPipeline accepting the following parameters: Object projectIdOrPath, String ref, Map<String, String> variables

See https://docs.gitlab.com/ee/api/pipelines.html#create-a-new-pipeline

[gmessner]

@SamerAdra
The documentation is very unclear on what the URL or form data should look like when variables are included, can you help by getting that information?

[gmessner]

@SamerAdra
I located the info I needed for this at https://docs.gitlab.com/ce/api/#array-of-hashes

This has been implemented and will be released in the next few days.

[gmessner]

@SamerAdra
Release 4.9.19 with this functionality has been released. Please verify and close when you have a chance.

[gmessner]

@SamerAdra
Since the enhancement has been released I am closing this issue, feel free to open it back up if you find any problems with the implementation.

[SamerAdra]

Sorry for waiting so long to test it. But I found out that it's not working when calling createPipeline with variables.
GitLab's API documentation on this does not help, but I found a comment in an issue that seems to help. Rémy Coutable suggests passing in the ref and variables as URL parameters, even though it's a POST call. I tried it out and it does seem to work that way.

org.gitlab4j.api.GitLabApiException: The following fields have validation errors: variables.key, base

at org.gitlab4j.api.AbstractApi.validate(AbstractApi.java:593)
at org.gitlab4j.api.AbstractApi.post(AbstractApi.java:319)
at org.gitlab4j.api.PipelineApi.createPipeline(PipelineApi.java:254)

[SamerAdra]

Because I don't see any way for me to reopen this issue, I created another one