Improve error message when secure connection cannot be established between  

Improve error message when secure connection cannot be established when adding MySQL with pmm-admin.

AC:

1. When secure connection cannot be established (due to IP/host verification failure). Instead of
   "Connection check failed: x509: cannot validate certificate for 127.0.0.1 because it doesn't contain any IP SANs." show easy to understand message.
2. Provide link to a guide/doc that explains why user sees that error and how to fix it.

Context: https://jira.percona.com/browse/PMM-8999?focusedCommentId=290132&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-290132