Add missing NGINXaaS certificate error descriptions and resolutions

[dylan-way]

Proposed changes

Problem: NGINXaaS returns various certificate errors to the user to assist them in fixing their deployments. Some of these user-facing errors point to this documentation but there isn't a corresponding certificate errors entry.

Solution: Adds the following error codes to the NGINXaaS certificate errors list:

• NoCertificateContent
• MissingContentType
• UnrecognizedContentType
• PKCS12ParseFailure
• PEMParseFailure

Closes Failed Customer Deployment Creation in swedencentral

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[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
_{Posted by the CLA Assistant Lite bot.}

[dylan-way]

I have hereby read the F5 CLA and agree to its terms

[ADubhlaoich]

LGTM!