Bug in refresh_individual_sex_affected

[holtgrewe]

Describe the bug
The command introduced in the resolution of #158 can crash.

To Reproduce

# python /usr/src/app/manage.py refresh_individuals
Refreshing all clinvar_xml individuals
Traceback (most recent call last):
  File "/usr/src/app/manage.py", line 29, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/__init__.py", line 419, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.8/site-packages/django/core/management/__init__.py", line 413, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/base.py", line 354, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/base.py", line 398, in execute
    output = self.handle(*args, **options)
  File "/usr/src/app/clinvar_export/management/commands/refresh_individuals.py", line 15, in handle
    refresh_individual_sex_affected()
  File "/usr/src/app/clinvar_export/models.py", line 405, in refresh_individual_sex_affected
    related_ped_entry = ped_entries[individual.name]
KeyError: '<REDACTED>'

Expected behavior
In this case, only a warning should be printed.

Additional context
N/A

[holtgrewe]

Root Cause Analysis
The assumption that the individual must be in the pedigree is wrong.

[holtgrewe]

Resolution Proposal
Check the existence of the individual in the Python dict. Print warning if it does not exist any more.

Affected Components
VarFish server

Affected Modules/Files
clinvar_export/models.py

Required Architectural Changes
None

Required Database Changes
None

Backport Possible?
Yes

Resolution Sketch
See above.