ci: improve gitlint (max line length in body with exceptions)

Follow-up of 5aa1540c5dc33d61020a08dd2818c0f5fd08575f but way more
mature. We now use custom gitlint rules written in Python to better
h

ci: improve gitlint (max line length in body with exceptions)

Follow-up of 5aa1540c5dc33d61020a08dd2818c0f5fd08575f but way more
mature. We now use custom gitlint rules written in Python to better
handle the max line length, with respect to a few valid exceptions.
Recognizing code blocks or compiler output, as discussed, is not
trivial and hard to get right for all corner-cases. Therefore, this
commit is a pragmatic way forward. The CI job should be kept optional.

Allowed exceptions for the 72 line length limit are now:

1. links in the following three common patterns:
https://example.com/very-long-links/very-long-links/very-long-links/very-long-links/very-long-links/very-long-links/very-long-links
[0] https://example.com/very-long-links/very-long-links/very-long-links/very-long-links/very-long-links/very-long-links/very-long-links
[0]: https://example.com/very-long-links/very-long-links/very-long-links/very-long-links/very-long-links/very-long-links/very-long-links

2. code blocks (anything between the three backticks)

```
let x = "very_long_very_long_very_long_very_long_very_long_very_long_very_long_very_long_very_long_very_long_"
```

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

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