Description of problem:
When generating reports of any variety, when it is to be sent to many email addresses, logs appear when the session object exceeds a given size:

[----] W, [2018-04-18T13:51:47.689723 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): Session object size of 182.9 KB exceeds threshold of 100 KB
[----] W, [2018-04-18T13:51:47.690012 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): _csrf_token <String> Size 44
[----] W, [2018-04-18T13:51:47.690110 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): all_sortcol <Fixnum> Size 8
[----] W, [2018-04-18T13:51:47.690229 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): all_sortdir <String> Size 4
[----] W, [2018-04-18T13:51:47.690308 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): breadcrumbs <Array> Size 81 Elements 1
[----] W, [2018-04-18T13:51:47.690393 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): browser <Hash> Size 111 Elements 5
[----] W, [2018-04-18T13:51:47.690459 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): changed <FalseClass> Size 3
[----] W, [2018-04-18T13:51:47.690537 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): css <Hash> Size 297 Elements 13
[----] W, [2018-04-18T13:51:47.690607 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): customer_name <String> Size 4
[----] W, [2018-04-18T13:51:47.696379 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button): edit <Hash> Size 148931 Elements 14
[----] W, [2018-04-18T13:51:47.702474 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button):   cb_cats <Hash> Size 803 Elements 20
[----] W, [2018-04-18T13:51:47.702645 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button):   cb_tenant <Hash> Size 175 Elements 13
[----] W, [2018-04-18T13:51:47.706729 #6028:16fb214]  WARN -- : MIQ(report_controller-x_button):   cb_users <Hash> Size 141488 Elements 2366
- - - - - 8< - - - - - 

This warning is triggered due to a hard-coded statement setting the threshold to 100kb:

  case Rails.env
  when "test", "development"
    SESSION_LOG_THRESHOLD = 50.kilobytes
    SESSION_ELEMENT_THRESHOLD = 5.kilobytes
  else
    SESSION_LOG_THRESHOLD = 100.kilobytes
    SESSION_ELEMENT_THRESHOLD = 10.kilobytes
  end

Customer monitoring utilities sometimes look for WARN statements and, even when this is expected behavior for their teams, they currently have no way to raise the session size thresholds to not WARN.

This RFE was requested so that we can manually configure a threshold.

Version-Release number of selected component (if applicable):
Any version (tested upstream)

How reproducible:
Every time.

Steps to Reproduce:
1. Have multiple email addresses (thousands) in which a report is generated to
2. Generate the report, view the messages in the log.

Actual results:
Warning prints statically at 100kb.

Expected results:
User should have some control over the warn threshold.

Additional info:
PR's are here, to both core repo (for settings) and classic UI:
https://github.com/ManageIQ/manageiq/pull/17334
https://github.com/ManageIQ/manageiq-ui-classic/pull/3831