Add custom cert troubleshooting page to AutoOps for self-managed docs

[wajihaparvez]

Summary

This PR adds a troubleshooting page to explain how to configure Elastic Agent with a custom SSL certificate. I added a new child page under the troubleshooting section to avoid overloading that page with info.

Closes https://github.com/elastic/opex-product/issues/666.

[github-actions]

Vale Linting Results

Summary: 3 suggestions found

💡 Suggestions (3)

File	Line	Rule	Message
deploy-manage/monitor/autoops/autoops-sm-custom-certification.md	15	Elastic.FutureTense	'will fail' might be in future tense. Write in the present tense to describe the state of the product as it is now.
deploy-manage/monitor/autoops/cc-cloud-connect-autoops-troubleshooting.md	26	Elastic.FirstPerson	Avoid first-person pronouns such as 'my'.
deploy-manage/monitor/autoops/cc-cloud-connect-autoops-troubleshooting.md	170	Elastic.FirstPerson	Avoid first-person pronouns such as 'my'.

[github-actions]

🔍 Preview links for changed docs

• deploy-manage/monitor/autoops/autoops-sm-custom-certification.md
• deploy-manage/monitor/autoops/cc-cloud-connect-autoops-troubleshooting.md

[arnonst]

@wajihaparvez

1. When user select to see the option of adding a variable and not hardcode the CR part.
   We show this sentence with a codeblock:

The following codeblock shows what your final configuration should look like. This example uses the second option, hardcoding the file path.

I think this part should not appear if the user is using the variable option as it may confuse the user who choose a different implementation of the change

2. We need to add the error x509 error "x509: certificate signed by unknown authority ..." also to the table

[kilfoyle]

LGTM! 🐇
Just a few super small suggestions.

[shainaraskas]

qq: should this be positioned as a troubleshooting page, or will some people come into this already knowing that they want a custom cert for elastic agent? wonder if we should take troubleshoot out of the title so people who already know what they want don't skip over this

[wajihaparvez]

@shainaraskas that's a good point. I've asked for clarification of the exact use case and I'll update accordingly

Update: It can go either way. Users could come to this page if they run into trouble OR if they already know their custom certificate is not trusted by the host machine. So I've moved this page out of the troubleshooting section and reworked it a bit, but I've also linked to it from the Troubleshooting page.

[arnonst]

@wajihaparvez
regarding:

We need to add the error x509 error "x509: certificate signed by unknown authority ..." also to the table

lets use the following to update the table:

• Error code: x509
• Error message - Certificate signed by unknown authority
• Description - Elastic Agent might not recognize your SSL certificate if it is signed by a custom or internal Certificate Authority (CA)