[Do not merge] Added-back-old-porting-guide-link-as-advised

[ssugandh]

Description

Adds back the old porting guide category and link for the PCCE/PCEE docs.

Motivation and Context

Usabilia feedback regarding broken link

How Has This Been Tested?

Tested on a local machine

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue) to add back an old link to the porting guide.

Checklist

• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes if appropriate.
• [x] All new and existing tests passed.

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Visit the preview URL for this PR (updated for commit 56ba671):

https://pan-dev-f1b58--pr326-hn6vacd1.web.app

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[Pubs-MV]

21.08 is old release and it is an EOL version. @ssugandh i don’t think we should add it pan.dev. Let’s talk about it in case I’m missing something.

We may need to ensure we have a different fix for any Admin Guides(after 21.08) that point to this guide.

cc: @csestito