Clean up makefile

[perdasilva]

[fgiloux]

Description

Background
As someone who wants to have a large community of contributors I would like that make is intuitive to use for building OLM, lowering the barrier to contribute. This means that targets are all meaningful, properly named and documented.

Implementation
A few things, i.e. `make test mentioned in this comment
A few improvements are in flight in this PR

Acceptance Criteria

• All make targets have a purpose
• Target names are explanatory
• Targets are documented through help and failure messages
• All checks have a purpose

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