Feedback from processing algorithms may be mistaken for plugin issue

[koebi]

Here's what I did

1. I issued an invalid request from the Directions from 1 Point Layer processing algorithm:
   My input layer had duplicate points, which traveling salesman optimization doesn't allow, but I turned on traveling salesman.

2. I issued a request from the same algorithm to the public API, but without configuring a key first.

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Here's what I got

As expected, the log contained information about the issue in both cases:

1. 
2. 

In both cases, this output seemed as if there was an issue with the plugin.
In both cases, the issue was not with the plugin, but with my input - one time it was faulty, one time I had no key configured.

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Here's what I think could be improved

How can we give feedback from the processing plugins in a way that tells the user that something is wrong that they can fix themselves, rather than it being an issue with the plugin?

[merydian]

QgsProcessingInfo.pushFormattedMessage could be benefitial here. It prints formatted HTML. We could keep the ordinary "developer" log message for people with those skills, but also provide Hints with links to further educational resources.