FIX: Always setting public files to true

[Blagoj5]

Problem

There is currently a bug in the code especially on line 46 where publicFIles is always true, e.g

config.publicFiles = false || true; // ALWAYS: true
config.publicFiles = true || true; // ALWAYS: true
config.publicFiles = eval('something else') || true; // throws an error and it was not handled

Solution

Make sure we do proper checking with the new util function setConfigField in case if the config value is string, undefined or an actual boolean. I didn't see a reason to really add tests for this, but if you guys want to do this, I can take care of it.

[Blagoj5]

I can't really tag reviewers, so I'll ping with this comment @Lith @dgmike :sweat_smile:

[codecov-commenter]

Codecov Report

Patch coverage: 54.54% and project coverage change: -3.04 :warning:

Comparison is base (b5fa17e) 81.48% compared to head (067688b) 78.44%.

:exclamation: Current head 067688b differs from pull request most recent head 6f47e5e. Consider uploading reports for the commit 6f47e5e to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #170 +/- ## ========================================== - Coverage 81.48% 78.44% -3.04% ========================================== Files 2 2 Lines 108 116 +8 ========================================== + Hits 88 91 +3 - Misses 20 25 +5 ``` | [Impacted Files](https://app.codecov.io/gh/strapi-community/strapi-provider-upload-google-cloud-storage/pull/170?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=strapi-community) | Coverage Δ | | |---|---|---| | [lib/provider.js](https://app.codecov.io/gh/strapi-community/strapi-provider-upload-google-cloud-storage/pull/170?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=strapi-community#diff-bGliL3Byb3ZpZGVyLmpz) | `78.07% <54.54%> (-3.07%)` | :arrow_down: |

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[Lith]

Thanks @Blagoj5 ! Could you please signing your commits ? I'm unable to merge without it :/

[Blagoj5]

It should be signed now, tell me if you have any problems. I wasn't aware this was an requirement sorry. @Lith