Fixes #1544. Adds _ASSERT for missing ExtData file

[mathomp4]

Description

Added an inquire and _ASSERT for ExtData2G Yaml files so we trap the missing file ourselves.

Related Issue

Closes #1544

Motivation and Context

Uses our traceback rather than depending on the compiler.

How Has This Been Tested?

I ran GEOS with and without it. It crashes with our traceback if not found:

pe=00091 FAIL at line=00073    ExtDataConfig.F90                        <could not find: GEOSachem_ExtData.yaml>
pe=00091 FAIL at line=00087    ExtDataConfig.F90                        <status=1>
pe=00091 FAIL at line=00052    ExtDataOldTypesCreator.F90               <status=1>
pe=00092 FAIL at line=00073    ExtDataConfig.F90                        <could not find: GEOSachem_ExtData.yaml>
pe=00092 FAIL at line=00087    ExtDataConfig.F90                        <status=1>
pe=00092 FAIL at line=00052    ExtDataOldTypesCreator.F90               <status=1>
pe=00093 FAIL at line=00073    ExtDataConfig.F90                        <could not find: GEOSachem_ExtData.yaml>
pe=00093 FAIL at line=00087    ExtDataConfig.F90                        <status=1>
pe=00093 FAIL at line=00052    ExtDataOldTypesCreator.F90               <status=1>
pe=00094 FAIL at line=00073    ExtDataConfig.F90                        <could not find: GEOSachem_ExtData.yaml>
pe=00094 FAIL at line=00087    ExtDataConfig.F90                        <status=1>
pe=00094 FAIL at line=00052    ExtDataOldTypesCreator.F90               <status=1>
pe=00095 FAIL at line=00073    ExtDataConfig.F90                        <could not find: GEOSachem_ExtData.yaml>
pe=00095 FAIL at line=00087    ExtDataConfig.F90                        <status=1>
pe=00095 FAIL at line=00052    ExtDataOldTypesCreator.F90               <status=1>
pe=00093 FAIL at line=00353    ExtDataGridCompNG.F90                    <status=1>
pe=00091 FAIL at line=00353    ExtDataGridCompNG.F90                    <status=1>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Trivial change (affects only documentation or cleanup)

Checklist:

• I have tested this change with a run of GEOSgcm (if non-trivial)
• I have added one of the required labels (0 diff, 0 diff trivial, 0 diff structural, non 0-diff)
• I have updated the CHANGELOG.md accordingly following the style of Keep a Changelog

[mathomp4]

And, of course, if @bena-nasa can think of more places for things like this, please add.