Save configuration after adding new provider

[maruiz93]

Related Jira ticket - CPAAS-5012 The GlobalConfiguration is resaved when a new provider is added. This solves an existing bug: when jenkins restart, it doesn't found the previously added providers and this cause job triggers listeners to stop working.

Testing done

Added the new testcase AddMessageProviderTest that checks:

• The added provided is included in the GlobalCIConfiguration
• The added provided keeps there even if a new GlobalCIConfiguration is loaded from configuration file.

Submitter checklist

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• [x] Ensure that the pull request title represents the desired changelog entry
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• [x] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[olivergondza]

Thanks for your contribution!

Having access to the internal bug tracker, I will note that this is observed IFF this method is called from init groovy script (this plugin never invokes addMessageProvider) and save is not called afterward.

In Jenkins, it is not guaranteed that every change to any Jenkins configurable entity will propagate to disk. It is a responsibility of a caller to make sure the objects changed gets saved once done manipulating it. (Jenkins makes no clear distinction which mutator methods do save internally, and which do not).

Though changing the semantics is not the way to go here. Think of clients that needs to add multiple providers that would result in disk save for each change. This flexibility really belongs to the caller side.