Add Alessio Caiazza as workhorse maintainer

Why is this change being made?

With this MR I'm officially proposing myself as a workhorse maintainer.

I've tracked my official activity as a trainee at #5357 (closed) but I've been involved in workhorse development and reviews since January 2018 (2 years).

I've contributed several MRs, mostly about handling uploads.

@jacobvosmaer-gitlab @nick.thomas do you think I'm ready for this? If not please provide me feedback on what should I improve.

Does this MR meet the acceptance criteria?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what

Closes #5357 (closed)