Addon dashboard Jenkins: provide a way to update the jenkins version from the UI

[florian-sanders-cc]

Context

In #1611 we added a new dashboard providing basic info about Jenkins.

We'd also like to provide a way to update the Jenkins version from the UI but this would be a different workflow than with typical operators.

The Jenkins update must be done from the Jenkins UI so our dashboards need to:

• get the info about a pending Update,
• if update is available, redirect to the Jenkins UI with a link.