Update GraphQL schema documentation

[pylipp]

I built the schema documentation that we host e.g. on api-staging.boxtribute.org/docs (instructions), and zipped it: docs.zip

Extract and view public/index.html.

[pylipp]

2.0 Improve documentation of graphQL schema

[codecov[bot]]

Codecov Report

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

Project coverage is 85.59%. Comparing base (0d473ab) to head (3c8232e). Report is 8 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1471 +/- ## ========================================== - Coverage 85.74% 85.59% -0.16% ========================================== Files 232 232 Lines 21912 21707 -205 Branches 1912 1914 +2 ========================================== - Hits 18789 18580 -209 - Misses 3086 3088 +2 - Partials 37 39 +2 ``` | [Flag](https://app.codecov.io/gh/boxwise/boxtribute/pull/1471/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boxwise) | Coverage Δ | | |---|---|---| | [backend](https://app.codecov.io/gh/boxwise/boxtribute/pull/1471/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boxwise) | `99.07% <ø> (-0.10%)` | :arrow_down: | | [frontend](https://app.codecov.io/gh/boxwise/boxtribute/pull/1471/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boxwise) | `82.35% <ø> (-0.21%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boxwise#carryforward-flags-in-the-pull-request-comment) to find out more.

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