C#: Add query for insecure certificate validation

[intrigus-lgtm]

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[ghsecuritylab]

Hello intrigus-lgtm 👋
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Happy hacking!

[intrigus-lgtm]

I would like to reduce FPs by doing something similar to Java:

codeql/java/ql/lib/semmle/code/java/security/UnsafeHostnameVerificationQuery.qll

Lines 80 to 104 in f9ae44c

	/**
	* Flags suggesting a deliberately unsafe `HostnameVerifier` usage.
	*/
	private class UnsafeHostnameVerificationFlag extends FlagKind {
	UnsafeHostnameVerificationFlag() { this = "UnsafeHostnameVerificationFlag" }
	bindingset[result]
	override string getAFlagName() {
	result
	.regexpMatch("(?i).*(secure|disable|selfCert|selfSign|validat|verif|trust|ignore|nocertificatecheck).*") and
	result != "equalsIgnoreCase"
	}
	}
	/** Gets a guard that represents a (likely) flag controlling an unsafe `HostnameVerifier` use. */
	private Guard getAnUnsafeHostnameVerifierFlagGuard() {
	result = any(UnsafeHostnameVerificationFlag flag).getAFlag().asExpr()
	}
	/** Holds if `node` is guarded by a flag that suggests an intentionally insecure use. */
	predicate isNodeGuardedByFlag(DataFlow::Node node) {
	exists(Guard g | g.controls(node.asExpr().getBasicBlock(), _) |
	g = getASecurityFeatureFlagGuard() or g = getAnUnsafeHostnameVerifierFlagGuard()
	)
	}

But as far as I know, there is no equivalent library for C#.