Add support for other git providers

[FatihYalmanbas]

Motivation
I would rather have repository-pr creation config to be abstracted so that I can use it for other git repository providers too. (Bitbucket, GitHub, GitLab, Internal git repository)

Possible Solution:
Maybe start with extracting github related parameters and PR checking logic to another class.
Maybe an extension called vcsProvider, where github is a function to preconfigure it. Just like mavenCentral in RepositoryHandler.
Then create a task for each repository configured in vcsProvider and make them depend on upgradeDependencies task. Can be named "upgradeDependenciesFor$vcsProviderName"

vcsProvider {
   github {
       token = ""
   }
}

Alternative to consider:
Maybe creating an output so other plugins or scripts can depend on this plugin to create their own logic. Such as uploading it to an internal server or in this case upgrading application dependencies and creating their own pr.