Create rule S6720(secrets): Zapier keys should not be disclosed (#2945)

You can preview this rule
[here](https://sonarsource.github.io/rspec/#/rspec/S6720/secrets)
(updated a few minutes after each push).

## Review

A dedicated reviewer checked the rule description successfully for:

- [ ] logical errors and incorrect information
- [ ] information gaps and missing content
- [ ] text style and tone
- [ ] PR summary and labels follow [the
guidelines](https://github.com/SonarSource/rspec/#to-modify-an-existing-rule)

---------

Co-authored-by: loris-s-sonarsource <loris-s-sonarsource@users.noreply.github.com>
Co-authored-by: Loris Sierra <loris.sierra@sonarsource.com>

rules/S6720/metadata.json

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+{
+}

rules/S6720/secrets/metadata.json

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+{
+  "title": "Zapier webhook URLs should not be disclosed",
+  "type": "VULNERABILITY",
+  "code": {
+    "impacts": {
+      "SECURITY": "HIGH"
+    },
+    "attribute": "TRUSTWORTHY"
+  },
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "30min"
+  },
+  "tags": [
+    "cwe",
+    "cert"
+  ],
+  "extra": {
+    "replacementRules": [
+
+    ]
+  },
+  "defaultSeverity": "Blocker",
+  "ruleSpecification": "RSPEC-6720",
+  "sqKey": "S6720",
+  "scope": "All",
+  "securityStandards": {
+    "CWE": [
+      798,
+      259
+    ],
+    "OWASP": [
+      "A3"
+    ],
+    "CERT": [
+      "MSC03-J."
+    ],
+    "OWASP Top 10 2021": [
+      "A7"
+    ],
+    "PCI DSS 3.2": [
+      "6.5.10"
+    ],
+    "PCI DSS 4.0": [
+      "6.2.4"
+    ],
+    "ASVS 4.0": [
+      "2.10.4",
+      "3.5.2",
+      "6.4.1"
+    ]
+  },
+  "defaultQualityProfiles": [
+    "Sonar way"
+  ],
+  "quickfix": "unknown"
+}

rules/S6720/secrets/rule.adoc

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+include::../../../shared_content/secrets/description.adoc[]
+
+== Why is this an issue?
+
+include::../../../shared_content/secrets/rationale.adoc[]
+
+=== What is the potential impact?
+
+Zapier webhook URLs have different effects depending on their permissions: They
+can be used only to write simple messages in instant messaging apps or trigger
+other advanced workflows.
+
+Below are some real-world scenarios that illustrate some impacts of an attacker
+exploiting the secret.
+
+include::../../../shared_content/secrets/impact/phishing.adoc[]
+
+include::../../../shared_content/secrets/impact/malware_distribution.adoc[]
+
+include::../../../shared_content/secrets/impact/codeless_vulnerability_chaining.adoc[]
+
+== How to fix it
+
+include::../../../shared_content/secrets/fix/revoke.adoc[]
+
+include::../../../shared_content/secrets/fix/vault.adoc[]
+
+=== Code examples
+
+:example_secret: https://hooks.zapier.com/hooks/catch/3017724/t0q8ed/
+:example_name: zapier_webhook_url
+:example_env: ZAPIER_WEBHOOK_URL
+
+include::../../../shared_content/secrets/examples.adoc[]
+
+//=== How does this work?
+
+//=== Pitfalls
+
+//=== Going the extra mile
+
+== Resources
+
+include::../../../shared_content/secrets/resources/standards.adoc[]
+
+//=== Benchmarks

shared_content/secrets/impact/codeless_vulnerability_chaining.adoc

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+==== Chaining of vulnerabilities
+
+Triggering arbitrary workflows can lead to problems ranging from a denial of
+service to worse, depending on how the webhook's data is handled. If the
+webhook performs a specific action that is affected by a vulnerability, the
+webhook acts as a remote attack vector on the enterprise.
+
+Components affected by this webhook could, for example, experience unexpected
+failures or excessive resource consumption. If it is a single point of failure
+(SPOF), this leak is critical.
+