Fix data_timezone when saving addupi telemetry

[aptiko]

When saving addupi telemetry, time zone was set to the empty string instead of "UTC", resulting in error when attempting to fetch the data.

Checklist:

• [ ] All tests are passing
• [ ] I have added any necessary documentation and/or release notes
• [ ] I have followed the commit message guidelines and the "before submitting a pull request" guidelines
• [ ] If I introduced (or abolished) any third-party library, I will write a short paragraph in this PR according to the guidelines
• [ ] I have removed all obsoleted code

[codecov[bot]]

Codecov Report

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

Comparison is base (64ab6c5) 98.17% compared to head (05b7b35) 98.18%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #515 +/- ## ======================================= Coverage 98.17% 98.18% ======================================= Files 41 41 Lines 2139 2145 +6 ======================================= + Hits 2100 2106 +6 Misses 39 39 ```

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