Add invalid announcements error widget and add related test (#2568)

[bstepanovski]

Fixes #2658

• Show invalid announcements as error alerts instead of failing silently.
• Adds error handling in Announcement#opts, updates the view to render a danger alert
• Includes an integration test for malformed YAML.

Also manually tested in the dashboard with both valid and invalid announcements.

[Bubballoo3]

The model updates here look good, but we are handling a bit too much logic in the view side. By checking validity in the controller and raising any errors from there, we will save a lot of code and headache in the views.

It looks like some of the other announcement tests are failing, so you will probably want to add an announcement to your dev dashboard to test it out manually and see what's going on. If you follow the trace of where the announcement path comes from, you'll see in UserConfiguration#announcement_path that it will read from an OOD_ANNOUNCEMENT_PATH environment variable before looking in the default locations. So you should be able to set this in a .env.local and point it to a file in your home directory.

[Bubballoo3]

We can just add this to announcement_views_test to keep things in one place

[Bubballoo3]

We typically want to do error checking in the controller (ApplicationController#set_announcements in this case)

[Bubballoo3]

We shouldn't have to make a new alert partial for this error, we can use a shared alert structure by calling flash.now from the controller.

[Bubballoo3]

This certainly looks better and it now does everything in the right place. Unfortunately something in FilesController seems to be snagging on the error and duplicating it every time a files/fs page attempts to load (the stacking is produced by clicking a favorites link from inside a files table view). In addition to duplicating the error message, it also stops the actual files request from responding properly. I will try to dig in and help narrow down what the actual issue is, but would love to know if you are able to replicate

Just to be clear, this should be a 'soft' error that alerts on every page but does not block any other code like it does here.