Prepare 1.2.0 release

[Annopaolo]

• [x] I have read CONTRIBUTING.md and CODE_OF_CONDUCT.md
• [x] I have added to CHANGELOG.md relevant changes and any other user facing change
• [x] I have added or ran the appropriate tests

What this PR does / why we need it:

Chores in order to get ready for the release of Astarte 1.2.0 (Salty Grasshopper)

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

Does this PR introduce a user-facing change?

• [ ] Yes
• [x] No

Additional documentation e.g. usage docs, diagrams, etc.:

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 69.42%. Comparing base (4690e5a) to head (13f6606). Report is 2 commits behind head on release-1.2.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release-1.2 #966 +/- ## =============================================== + Coverage 68.18% 69.42% +1.24% =============================================== Files 281 263 -18 Lines 7437 7088 -349 =============================================== - Hits 5071 4921 -150 + Misses 2366 2167 -199 ```

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