Improve AzureDevOps connection logs

WHY

Azure DevOps connection may fail for several reasons.

We are authenticating against ADO when defining Global DevOps Platform settings, and also when providing a PAT for Project Import.

We should improve the logs of these operations to provide a better insight on what's happening when the connection does not work.

WHAT

The user must be able to determine if there is a problem coming from

• The target URL
• The token/permissions
• The security (SSL certificate) (out of scope for this ticket)
• The use of something not supported (ex: TFVC version control protocol) (out of scope for this ticket)

Ideally, the logs should explicit:

• If an SSL error happened (out of scope for this ticket)
  • This can be the case if the JRE/JDK running SonarQube doesn't have the CA certificate used by the Azure DevOps server loaded
• If the token has expired
• If the token does not have the right permission
• If the URL is invalid
• If the target SCM is something else than Git (ex: TFVC, which we don't support) (out of scope for this ticket)
• If the target PR to decorate does not exist
• If the target branch to analyse does not exist (out of scope for this ticket)

SonarQube should log 

• every PR decoration failed attempts with
• Target server URL
• Target collection/organisation
• Current token permission (if possible) (out of scope for this ticket)
• Presence of any SSL certificate or proxy (out of scope for this ticket)
• PR reference number

• all connection failed attempts with
  • target server URL
  • target collection/organization
  • presence of any SSL certificate or proxy (out of scope for this ticket)
  • any error messages related