Deprecate sonar.http.timeout (replaced by sonar.scanner.connectTimeout)

[martin-strecker-sonarsource]

The newly introduced timeouts (#1977) for the scanner overlap with our sonar.http.timeout setting (#1878). It is unfortunate that there are four user-facing settings for essentially the same thing. We can not do much about the three new settings as they are defined for all scanners. But we can at least reduce the number of settings from four to three by deprecating our sonar.http.timeout setting.
Actions:

• Add a warning about the deprecation of sonar.http.timeout with a hint about the replacement sonar.scanner.connectTimeout (see also Add support for JRE provisioning: HttpClient timeouts #1977)
• Update the documentation
• Turn the usage of sonar.http.timeout into an error on the next major release after the deprecation warning was introduced and remove the support for sonar.http.timeout