[WAF] Clarify possibility of acting on truncated payloads (#19105)

* Clarify that truncated requests can be actioned via a Custom Rule even with the max size limit

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Co-authored-by: Pedro Sousa <[email protected]>

Author: Vortexmind

src/content/docs/waf/managed-rules/index.mdx

@@ -51,3 +51,5 @@ At the zone level, you can only deploy each WAF managed ruleset once. At the [ac
 ## Important remarks
 
 Cloudflare analyzes the body of incoming requests up to a certain maximum size that varies according to your Cloudflare plan. For Enterprise customers, the maximum body size is 128 KB, while for other plans the limit is lower. This means that the behavior of specific managed rules that analyze request bodies can vary according to your current Cloudflare plan.
+
+If included in your plan, you can use [request body fields](/ruleset-engine/rules-language/fields/http-request-body/) such as `http.request.body.truncated` or `http.request.headers.truncated` in [custom rules](/waf/custom-rules/) that apply appropriate actions to requests that have not been fully analyzed by Cloudflare due to the maximum body size.