fix: switch to pdftohtml for pdf to html conversions

[sbplat]

Description

Switch from LibreOffice to pdftohtml for PDF to HTML conversions.

Closes #567

Checklist:

• I have read the Contribution Guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

Contributor License Agreement

By submitting this pull request, I acknowledge and agree that my contributions will be included in Stirling-PDF and that they can be relicensed in the future under the MPL 2.0 (Mozilla Public License Version 2.0) license.

(This does not change the general open-source nature of Stirling-PDF, simply moving from one license to another license)

[Frooodle]

is pdftohtml in docker image?

[Frooodle]

Also sonarcloud can be ignored, its more just for visability to judge yourself if you want to do code changes

[sbplat]

is pdftohtml in docker image?

Not sure. Should add it to be safe.

[Frooodle]

I only want to add depending on how large the dependencies are vs the results it has etc

I know the optional install we have of calibre could also support this

[sbplat]

The optional install of calibre uses poppler to convert pdf to html, so it should be the same.

[sonarqubecloud]

Quality Gate failed

Failed conditions
2 Security Hotspots
33.3% Duplication on New Code (required ≤ 3%)
E Reliability Rating on New Code (required ≥ D)

See analysis details on SonarCloud

Catch issues before they fail your Quality Gate with our IDE extension SonarLint

[Frooodle]

LGTM