Add a SKILL and PROMPT for generating rules with AI (#1557)

Signed-off-by: Cosmin Cojocar <cosmin@cojocar.ch>

.github/prompts/create-gosec-rule.prompt.md

@@ -0,0 +1,34 @@
+---
+name: Create Gosec Rule
+mode: agent
+description: Create a new gosec rule from a Go issue description using the reusable gosec skill.
+---
+
+Use the skill Create New Gosec Rule from .github/skills/gosec-new-rule/SKILL.md.
+
+Follow the skill contract exactly:
+- First response must propose a rule ID, implementation approach, relevance for Go 1.25 and Go 1.26, and ask for confirmation.
+- Do not start implementation until confirmation is explicitly provided.
+
+Issue description:
+
+### Summary
+{{summary}}
+
+### Steps to reproduce the behavior
+{{steps_to_reproduce}}
+
+### gosec version
+{{gosec_version}}
+
+### Go version (output of 'go version')
+{{go_version}}
+
+### Operating system / Environment
+{{environment}}
+
+### Expected behavior
+{{expected_behavior}}
+
+### Actual behavior
+{{actual_behavior}}