`--debug_parser` does not use `LangServer:::_load_config_file`, hardcodes `.fortlsrc`

[phil-blain]

Describe the bug

Using --debug_parser, only .fortlsrc is used, other accepted config file names are ignored.

To Reproduce
This assumes the latest version (2.13) is installed using pip install --user

• Use .fortls as a config file in $PWD
• python -m pdb $(which fortls) --debug_parser --debug_rootpath=$PWD --debug_filepath some/fortran/file.F90
• b /path/to/home/.local/lib/python3.8/site-packages/fortls/__init__.py:447 (function debug_server_parser)
• c
• p args.config

Expected behavior
See .fortls

Setup information (please complete the following information):

• OS: Linux
• Python Version 3.8
• fortls Version 2.13
• Code editor used: irrelevant for this bug
• the Fortran extension for the code editor and its version: irrelevant

Configuration information (please complete the following information):

• Your .fortlsrc or .fortls.json or .fortls configuration file OR any other JSON config being used (if any)

does not matter for this bug