ENH: Give more informative file format errors

[mferrera]

Resolves #706

This will list some potential file formats, which are not complete in their file extensions permutations but should be sufficient enough to give a hint as to what kind of required.

[codecov-commenter]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (33652a2) 80.08% compared to head (b51d79e) 80.06%.

Files	Patch %	Lines
src/xtgeo/well/_well_aux.py	25.00%	2 Missing and 1 partial :warning:
src/xtgeo/grid3d/_grid_import.py	60.00%	2 Missing :warning:
src/xtgeo/grid3d/grid_property.py	33.33%	2 Missing :warning:
src/xtgeo/surface/regular_surface.py	33.33%	2 Missing :warning:
src/xtgeo/xyz/points.py	33.33%	2 Missing :warning:
src/xtgeo/xyz/polygons.py	33.33%	2 Missing :warning:
src/xtgeo/io/_file.py	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1165 +/- ## ========================================== - Coverage 80.08% 80.06% -0.02% ========================================== Files 97 97 Lines 13612 13634 +22 Branches 2186 2187 +1 ========================================== + Hits 10901 10916 +15 - Misses 1981 1988 +7 Partials 730 730 ```

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