Add a flag to search job with appended results

[ramonfigueiredo]

• Add a new configuration option search_jobs.append_results in cuegui.yaml to control job search behaviour.
• If search_jobs.append_results is set to true, search results will be appended to the current list of monitored jobs.
• If search_jobs.append_results is set to false, the existing jobs will be cleared before displaying the search results.
• Updated Constants.py to include the new configuration parameter.
• Modified MonitorJobsPlugin.py to conditionally clear the job monitor based on the config setting.

[ramonfigueiredo]

I've suggested a new description for the new flag to make it clearer.

Done, thanks!