feat: add REST API endpoints for manipulation of Access Form elements and sections

[RadovanTomik]

Negotiator pull request:

Description:

Aadd REST API endpoints for manipulation of Access Form elements and sections. To test them please use swagger.

Checklist:

Make sure you tick all the boxes bellow if they are true or do not apply:

• [x] I have performed a self review of my code
• [x] My code follows Google Java Code style
• [x] I have made my code as simple as possible
• [x] I have added unit tests and the code coverage has not decreased
• [x] I have updated the documentation in all relevant places

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.06931% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 78.45%. Comparing base (8a2076c) to head (391117f). Report is 15 commits behind head on master.

Files	Patch %	Lines
...ric/negotiator/dto/access_form/ElementMetaDTO.java	77.77%	2 Missing :warning:
...ric/negotiator/dto/access_form/SectionMetaDTO.java	75.00%	2 Missing :warning:
...gotiator/dto/access_form/AccessFormElementDTO.java	0.00%	1 Missing :warning:
...c/negotiator/dto/access_form/ElementCreateDTO.java	87.50%	1 Missing :warning:
...c/negotiator/dto/access_form/SectionCreateDTO.java	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #289 +/- ## ============================================ + Coverage 77.93% 78.45% +0.52% - Complexity 909 973 +64 ============================================ Files 125 133 +8 Lines 2773 2892 +119 Branches 161 163 +2 ============================================ + Hits 2161 2269 +108 - Misses 512 522 +10 - Partials 100 101 +1 ``` | [Flag](https://app.codecov.io/gh/BBMRI-ERIC/negotiator/pull/289/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BBMRI-ERIC) | Coverage Δ | | |---|---|---| | [unit](https://app.codecov.io/gh/BBMRI-ERIC/negotiator/pull/289/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BBMRI-ERIC) | `78.45% <93.06%> (+0.52%)` | :arrow_up: | 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=BBMRI-ERIC#carryforward-flags-in-the-pull-request-comment) to find out more.

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