Add the jTDS built-in driver deprecated message

[hiroyuki-sato]

Relates to #267. Remove the jTDS built-in driver in an upcoming release.

[dmikurube]

• It'd be better in general to show such a warning earlier. How about put the log there?
  • https://github.com/embulk/embulk-input-jdbc/blob/6cb64d0f9ac6671df802d2d326ea662e6743c0bb/embulk-input-sqlserver/src/main/java/org/embulk/input/sqlserver/SQLServerInputPlugin.java#L136
• Logging in two lines (two log records) could confuse users when the logging is busy. Let's merge this in a single log line. For example:
  • "driver_type: jtds" is specified, but note that the jTDS built-in driver will be removed at some point in the future. Please see https://github.com/embulk/embulk-input-jdbc/issues/267

[hiroyuki-sato]

@dmikurube Sorry for late reply. I realized the driver_path support needs some source modification. This part also need modify. I'm preparing #269 and #270. Convert to draft for a while.