Added exporter

[fadiga]

Fixes #77

[kelson42]

At which stage the quality assessment of this new feed will be checked (against current one)?

[codecov[bot]]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (7354663) compared to base (237bd5e). Patch coverage: 100.00% of modified lines in pull request are covered.

:exclamation: Current head 7354663 differs from pull request most recent head b045584. Consider uploading reports for the commit b045584 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #90 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 15 17 +2 Lines 544 567 +23 ========================================= + Hits 544 567 +23 ``` | [Impacted Files](https://codecov.io/gh/openzim/cms/pull/90?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim) | Coverage Δ | | |---|---|---| | [backend/src/backend/constants.py](https://codecov.io/gh/openzim/cms/pull/90/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim#diff-YmFja2VuZC9zcmMvYmFja2VuZC9jb25zdGFudHMucHk=) | `100.00% <100.00%> (ø)` | | | [backend/src/backend/exporters/\_\_init\_\_.py](https://codecov.io/gh/openzim/cms/pull/90/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim#diff-YmFja2VuZC9zcmMvYmFja2VuZC9leHBvcnRlcnMvX19pbml0X18ucHk=) | `100.00% <100.00%> (ø)` | | | [...end/src/backend/exporters/kiwix\_public\_exporter.py](https://codecov.io/gh/openzim/cms/pull/90/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim#diff-YmFja2VuZC9zcmMvYmFja2VuZC9leHBvcnRlcnMva2l3aXhfcHVibGljX2V4cG9ydGVyLnB5) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim)

:umbrella: View full report at Codecov.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.