Add Observed Examples

[cpholguera]

Add to maswe.instructions.md

- **observed_examples**: Links to public, real-world occurrences of the weakness (e.g. CVE entries or published research). Optional.

Draft content:

observed_examples.patch

Apply with:

git apply observed_examples.patch

Review the draft content, correct and add more wherever possible.

[cpholguera]

We are considering including here the "Example Attack Scenarios" we started adding (and then removed) from MASTG tests. See

• https://github.com/OWASP/mastg/pull/3872/changes#diff-b521d249dba3d24f0976ac4f739af5f8c29884118bc6a2b76659dfb6cadd2cfb
• https://github.com/OWASP/mastg/pull/3873/changes#diff-9cc012be5cfd1157a5752e5a1983c2906aa8f52d33918aaec78362348d8593ae