Improve Performance of Log Downloads

Current Situation

• The JobScheduler main log is offered for download with ./jobscheduler/log API.
• This API results in an OutOfMemoryError if the main log is too big as the log is stored in memory of the web service before being delivered to the client.
• It depends on the Java option -Xmx, which specifies the maximum size of the memory allocation pool.
• JOC's Jetty is started with -Xmx512m per default which causes an OutOfMemoryError being raised for main logs larger than about 100MB.

Desired Behavior

• An OutOfMemoryError should not be raised for at least main logs <= 1GB.
• The processing of logs for download is changed to make use of two separate API requests:
  • Info Request: the main log is requested from the Master and is stored to a temporary file. File size and meta data are returned when calling this API
  • Download Request: the temporary file is directly downloaded without any additional meta data.
• The log file download should behave as any download and allow the client browser to display the progress of transfer.
• Order and Task logs will be offered for download too with JOC-435.

Maintainer Notes

• The ./jobscheduler/log API requested first the JobScheduler main log at the JobScheduler.
• At some point you reach other limits e.g. the web server of the JobScheduler doesn't respond to the JOC Cockpit web service because of a SocketTimeoutException if the log is larger than 1GB.