[Snyk] Security upgrade @slack/client from 3.9.0 to 4.0.0

[lmammino]

This PR was automatically created by Snyk using the credentials of a real user.

Snyk has created this PR to fix one or more vulnerable packages in the `yarn` dependencies of this project.

Changes included in this PR

• Changes to the following files to upgrade the vulnerable dependencies to a fixed version:
  • package.json
  • yarn.lock

Note for zero-installs users

If you are using the Yarn feature zero-installs that was introduced in Yarn V2, note that this PR does not update the .yarn/cache/ directory meaning this code cannot be pulled and immediately developed on as one would expect for a zero-install project - you will need to run yarn to update the contents of the ./yarn/cache directory. If you are not using zero-install you can ignore this as your flow should likely be unchanged.

Vulnerabilities that will be fixed

With an upgrade:

Severity	Priority Score (*)	Issue	Breaking Change	Exploit Maturity
	646/1000 Why? Proof of Concept exploit, Has a fix available, CVSS 6.5	Server-side Request Forgery (SSRF) SNYK-JS-REQUEST-3361831	Yes	Proof of Concept
	696/1000 Why? Proof of Concept exploit, Has a fix available, CVSS 7.5	Regular Expression Denial of Service (ReDoS) SNYK-JS-SEMVER-3247795	Yes	Proof of Concept
	646/1000 Why? Proof of Concept exploit, Has a fix available, CVSS 6.5	Prototype Pollution SNYK-JS-TOUGHCOOKIE-5672873	Yes	Proof of Concept

(*) Note that the real score may have changed since the PR was raised.

Check the changes in this PR to ensure they won't cause issues with your project.

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Learn how to fix vulnerabilities with free interactive lessons:

🦉 Server-side Request Forgery (SSRF) 🦉 Regular Expression Denial of Service (ReDoS) 🦉 Prototype Pollution