* Add support for link type between issues

Fixes #847

* Create AbstractIssue

* Add repository submodules api

Fixes #921

* Fix unit test

Fixes #883

Fixes #887

Fixes #936

Co-authored-by: Ипполитов Вадим Дмитриевич <vippolitov@poidem.ru>

Co-authored-by: Jérémie Bresson <dev@jmini.fr>

Co-authored-by: Michael Fitoussi <16884890+mifitous@users.noreply.github.com>

* Added ReleaseLinks API (#639)

* Deprecate the "external" attribute in Link

* Add tests

* Rename to ReleaseLinksApi and add the getter in GitLabApi

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Co-authored-by: Jeremie Bresson <jeremie.bresson@unblu.com>

* Added hook and fetch capabilities

* Fix tests

* Remove superfluous formatting

Co-authored-by: Jeremie Bresson <jeremie.bresson@unblu.com>

Fixes #889

Add iterationTitle in IssueFilter for filtration issues
by this field

Co-authored-by: Усачев Дмитрий Дмитриевич <92usachevdd@region.cbr.ru>

* feat(scheduled-pipeline): makes scheduled pipelines runnable

* Update src/main/java/org/gitlab4j/api/PipelineApi.java

Co-authored-by: Jérémie Bresson <dev@jmini.fr>

* fix(scheduled-pipeline): change post()-call

* Update src/main/java/org/gitlab4j/api/PipelineApi.java

Co-authored-by: Jérémie Bresson <dev@jmini.fr>

* Add missing import

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Co-authored-by: Jérémie Bresson <dev@jmini.fr>
Co-authored-by: Jeremie Bresson <jeremie.bresson@unblu.com>
Co-authored-by: Ruben Vitt <dev@rubeen.one>

* Add ExternalStatusCheckApi

Fixes #919

* Add ExternalStatusCheckEvent

* Fix javadoc

Co-authored-by: Jérémie Bresson <dev@jmini.fr>

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Co-authored-by: jason <jason.irwin@idoxgroup.com>

Co-authored-by: Vladimir Krumov <vladimir.krumov@paysafe.com>

Fixed de-serialization of MembershipSourceType by letting the JacksonJsonEnumHelper know that the first letter should be capitalized

This makes it possible to stream data coming
from another server straight into the POST request to Gitlab,
saving an extra, expensive, and useless IO operation on disk.

Fix #769

Adding branches_to_be_notified to SlackService and deprecating notify_only_default_branch as per
https://docs.gitlab.com/ee/api/services.html#createedit-slack-service

A 'scope' attribute was added to the Events API that allows retrieval of all events for a user across all the projects that user has access to.  This change adds support for this new attribute.