[Hylte] Add cobrand

[jonkri]

Hylte kommun is a municipality in Sweden. Their cobrand is running on https://hylte.fixamingata.se/. The empty public_update.html file is intentional (we are currently not using this section of the inspect form).

• [ ] Has the code POD documentation been added or updated?
• [ ] Whether this PR should include changes to any public documentation, or the FAQ;
• [x] All cobrand-specific commits start their commit message with the cobrand in square brackets;
• [ ] Is new functionality tested? CodeCov will warn you about the diff coverage, but won’t complain about e.g. new files;
• [ ] Will cobrand-specific changes require additional work to ensure consistent behaviour on www.fixmystreet.com?
• [ ] Are the changes tested for accessibility?
• [ ] Have you updated the changelog? If this is not necessary, put square brackets around this: [skip changelog]

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 15.90909% with 37 lines in your changes missing coverage. Please review.

Project coverage is 54.88%. Comparing base (ce80472) to head (151e66e). Report is 181 commits behind head on master.

Files	Patch %	Lines
perllib/FixMyStreet/Cobrand/Hylte.pm	17.94%	32 Missing :warning:
perllib/FixMyStreet/Cobrand/FixaMinGata.pm	0.00%	5 Missing :warning:

:exclamation: There is a different number of reports uploaded between BASE (ce80472) and HEAD (151e66e). Click for more details.

HEAD has 14 uploads less than BASE

| Flag | BASE (ce80472) | HEAD (151e66e) | |------|------|------| ||15|1|

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5048 +/- ## =========================================== - Coverage 82.65% 54.88% -27.78% =========================================== Files 396 343 -53 Lines 30828 25131 -5697 Branches 4890 4740 -150 =========================================== - Hits 25482 13793 -11689 - Misses 3900 10018 +6118 + Partials 1446 1320 -126 ```

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