Update doc content on setting up Squid proxy server

Description:

Regarding the steps provided in doc [1] to set up Squid, it is better if we can provide steps for mac, ubuntu and windows users. I have tried following the doc for Mac and I installed Squid using brew install squid, and that was it. I was good to go without moving to step 2 (atleast to achieve my end goal). Can we evaluate the relevance of step 2? and if needed, better to update the step 2 for mac, ubuntu and windows.

Also, noticed that I didn't need to navigate to the provided installation guide to set up Squid (refer to step 1 in doc [2]). Maybe we can re-evaluate the content that needs to go into this doc and revamp the current doc.

[1] https://apim.docs.wso2.com/en/latest/install-and-setup/setup/mi-setup/enabling_ssl_tunneling_thru_proxy_server/
[2] Step 1: Install Squid as described [here](http://wiki.squid-cache.org/SquidFaq/InstallingSquid)

Read the setup guide at https://apim.docs.wso2.com/en/latest/install-and-setup/setup/mi-setup/enabling_ssl_tunneling_thru_proxy_server/ and review its Squid installation steps, including the linked Squid installation guide. Compare the Mac, Ubuntu, and Windows setup paths and decide whether step 2 is needed; done means the document has clear, relevant platform-specific instructions without unnecessary links or steps.