Add hostname param support for tls servername

[BoringCat]

Modified for this case

• need to monitor multiple domain which is dynamic resolve to different instance
• instance handle multiple certificate and distinguish with SNI

To monitor more than thousands domain. I can not just create config for prometheus and blackbox-exporter dynamiced. If each domain need it own job and module. The config file will to large and may be affect prometheus performance.

So it will be perfect if single module can handle all request just with hostname param like http probe 👍

[roidelapluie]

Thanks. This would require tests.

[electron0zero]

fyi: #981 is also fixing the same issue.

[BoringCat]

fyi: #981 is also fixing the same issue.

Well, after i make this PR. My target was changed. I need to known more infomation about the certificate. I'm now creating my own exporter. So I have no time work for this. If #981 can fix it and pass test. Please close this.

[electron0zero]

fyi: #981 is also fixing the same issue.

Well, after i make this PR. My target was changed. I need to known more infomation about the certificate. I'm now creating my own exporter. So I have no time work for this. If #981 can fix it and pass test. Please close this.

closing in favor of #981