feat/attachment_pdf_merger

[jungwire]

Negotiator pull request:

Description:

Adds Doc and Docx conversion for merged PDF download

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
• [ ] I have added unit tests and the code coverage has not decreased
• [ ] I have updated the documentation in all relevant places

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 12.50000% with 21 lines in your changes missing coverage. Please review.

Please upload report for BASE (canserv-poc@ac62c18). Learn more about missing BASE report.

Files	Patch %	Lines
...c/negotiator/service/AttachmentMergingService.java	0.00%	21 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## canserv-poc #369 +/- ## ============================================== Coverage ? 79.81% Complexity ? 1233 ============================================== Files ? 162 Lines ? 3794 Branches ? 208 ============================================== Hits ? 3028 Misses ? 619 Partials ? 147 ``` | [Flag](https://app.codecov.io/gh/BBMRI-ERIC/negotiator/pull/369/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/369/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BBMRI-ERIC) | `79.81% <12.50%> (?)` | | 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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