feat: add psp fsgroup module

Signed-off-by: peefy <[email protected]>

psp-fsgroup/README.md

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+## Introduction
+
+`psp-fsgroup` is a kcl PSP validation package.
+
+## Resource
+
+Code source and document is [here](https://github.com/kcl-lang/artifacthub/tree/main/psp-fsgroup)

psp-fsgroup/kcl.mod

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+[package]
+name = "psp-fsgroup"
+version = "0.1.0"
+description = "`psp-fsgroup` is a kcl validation package"
+

psp-fsgroup/main.k

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+"""Controls the user and group IDs of the container and some volumes.
+Corresponds to the `runAsUser`, `runAsGroup`, `supplementalGroups`, and
+`fsGroup` fields in a PodSecurityPolicy. For more information, see
+https://kubernetes.io/docs/concepts/policy/pod-security-policy/#users-and-groups
+"""
+
+type Rule = "MustRunAs" | "MustRunAsNonRoot" | "RunAsAny"
+FIELDS = ["runAsUser", "runAsGroup", "supplementalGroups", "fsGroup"]
+
+schema Params:
+    rule: Rule
+    ranges: [Range]
+
+schema Range:
+    min: int
+    max: int
+
+    check:
+        min <= max
+
+params: Params = option("params")
+
+# Define the validation function
+validate = lambda item: {str:} {
+    if item.kind == "Pod":
+        fg = item?.spec?.securityContext?.fsGroup
+        if params.rule == "RunAsAny":
+            assert True
+        # MustRunAs - Validates pod spec fsgroup against all ranges
+        elif params.rule == "MustRunAs":
+            assert fg and all range in params.ranges {
+                range.min <= fg <= range.max
+            }
+        # Validates pod spec fsgroup against all ranges or allow pod spec fsgroup to be left unset
+        elif params.rule == "MayRunAs" and fg:
+            assert all range in params.ranges {
+                range.min <= fg <= range.max
+            }
+    # Return the resource
+    item
+}
+# Validate All resource
+items = [validate(i) for i in option("items")]