feat: --rating-only flag to only test checks required for rating

[magnuslarsen]

Describe your changes

Fixes #2875

UPDATES since #2942:

• Switched to --rating-only for consistency with the rest of the testssl.sh
• Moved the flag in the help-text
• Set VULN_THRESHLD to -1 to force the vuln. checks to appear under the same header (zero was not enough?)
• Added some docs, albeit basic :--)

Added a very simple --rating-only flag, that will enable only the checks required for rating to be successful.

NOTE: this is a very simple implementation that sets the required variables to true (even if they potentially were disabled with other flags). HOWEVER it is also possible to add additional tests with any of the single-check flags (like ./testssl.sh --rating-only --winshock)

Not sure if this is too simple for your liking? Let me know if so, then I will update. I threw this together rather quickly :-)

...oh, and I lowercased the --disable-rating help text; all the surrounding text is lowercase

What is your pull request about?

• Bug fix
• Improvement
• New feature (adds functionality)
• Breaking change (bug fix, feature or improvement that would cause existing functionality to not work as expected)
• Typo fix
• Documentation update
• Update of other files

If it's a code change please check the boxes which are applicable

• For the main program: My edits contain no tabs, indentation is five spaces and any line endings do not contain any blank chars
• I've read CONTRIBUTING.md and Coding_Convention.md
• I have tested this fix or improvement against >=2 hosts and I couldn't spot a problem
• I have tested this new feature against >=2 hosts which show this feature and >=2 host which does not (in order to avoid side effects) . I couldn't spot a problem
• For the new feature I have made corresponding changes to the documentation and / or to help()
• If it's a bigger change: I added myself to CREDITS.md (alphabetical order) and the change to CHANGELOG.md

[drwetter]

👍🎉

One thing: --rating-only can be taken differently. Maybe --rating-minimum? Optionally: if you have pandoc installed you just have to go to doc and issue make in order to make the HTML and (t)roff file.

Otherwise I can do both next days...

[drwetter]

Let's leave that for now at least. Thanks a lot!

[magnuslarsen]

Thanks Dirk! I do have pandoc, i was just not in time it seems :--)

[drwetter]

Don´t want to hold you back, PRs are open to everyone ;-)