fix: allow administrators to post comments during approval phase

[RadovanTomik]

Negotiator pull request:

Description:

Checklist:

Make sure you tick all the boxes below if they are true or do not apply before you ask for review

• [x] I have performed a self-review of my code
• [x] I have made my code as simple as possible
• [x] I have added relevant tests for my changes and the code coverage has not dropped substantially
• [x] I have removed all commented code
• [x] I have updated the documentation in all relevant places (Javadoc, Swagger, MDs...)
• [x] I have described the PR and added a meaningful title in the Conventional Commits format

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.47%. Comparing base (4a81f8e) to head (36e7adc).

Files	Patch %	Lines
...bbmri_eric/negotiator/service/PostServiceImpl.java	92.30%	0 Missing and 1 partial :warning:
...egotiator/service/UserNotificationServiceImpl.java	50.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #362 +/- ## ============================================ - Coverage 80.59% 80.47% -0.13% + Complexity 1228 1224 -4 ============================================ Files 160 160 Lines 3716 3728 +12 Branches 203 205 +2 ============================================ + Hits 2995 3000 +5 - Misses 575 577 +2 - Partials 146 151 +5 ``` | [Flag](https://app.codecov.io/gh/BBMRI-ERIC/negotiator/pull/362/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/362/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BBMRI-ERIC) | `80.47% <86.66%> (-0.13%)` | :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=BBMRI-ERIC#carryforward-flags-in-the-pull-request-comment) to find out more.

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