Added cost func to the list of options displayed in log file

[AndrewLister-STFC]

Description of work

The log file didn't output which cost func was used

Fixes #

Testing Instructions

Checklist

• The title is of a format appropriate for a line in future release notes.
• I have added the appropriate tags to the PR.
• My PR represents one logical piece of work.
• My PR fully fixes the issue linked. If new issues have been created, what are they?
• I have added the appropriate tests to cover code that has been added.
• I have updated the documentation in the relevant places to cover the changes.

[coveralls]

coverage: 90.832%. remained the same
when pulling 03577fc on cost_func_options_write
into 76eb8d7 on master.

[github-actions]

Unit & System Test Results

  4 files  ±0    4 suites  ±0   6m 42s ⏱️ +4s
502 tests ±0  494 ✅ ±0   8 💤 ±0  0 ❌ ±0 
958 runs  ±0  904 ✅ ±0  54 💤 ±0  0 ❌ ±0 

Results for commit 03577fc. ± Comparison against base commit 76eb8d7.

♻️ This comment has been updated with latest results.