fix: use fixed uid/gid 5000:5000 for all tesseracts (#102)

#### Relevant issue or PR
Fixes #101 

#### Description of changes
☝️ 

#### Testing done
CI

#### License

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license](https://pasteurlabs.github.io/tesseract/LICENSE).
- [x] I sign the Developer Certificate of Origin below by adding my name
and email address to the `Signed-off-by` line.

<details>
<summary><b>Developer Certificate of Origin</b></summary>

```text
Developer Certificate of Origin
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Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.


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(a) The contribution was created in whole or in part by me and I
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</details>

Signed-off-by: Dion Häfner <dion.haefner@simulation.science>

Author: dionhaefner

tesseract_core/sdk/templates/Dockerfile.base

@@ -54,7 +54,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 {% endif %}
 
 # Drop to a non-root user
-RUN useradd --create-home -s /bin/bash tesseractor
+RUN groupadd -g 5000 tesseractor && \
+    useradd -u 5000 -g 5000 --create-home -s /bin/bash tesseractor
 WORKDIR /tesseract
 RUN chown tesseractor:tesseractor /tesseract
 USER tesseractor