Previous behavior was that the value of .Params.portrait (defined in
markdown front matter) was treated as a glob pattern. If
Params.portrait was nil, "*thumbnail*" would be used by default.
This commit changes the behavior to use the following resolution
order: .Params.portrait (verbatim), "*portrait*", "*thumbnail*".
In current practice, only two names are used for images:
"portrait.(jpg|webp)" and "thumbnail.(jpg|webp)". Usually, portrait is
larger and thumbnail is cropped. Most contributor pages declare
"portrait.(jpg|webp)" explicitly in the front matter.
If current naming patterns remain in use, this change should make
declaring .Params.portrait basically obsolete, unless a really custom
file name is used (in such case, the manual override remains
available). As far as defaults go, a larger image is likely preferred
on a "profile" page.
This should also help auto-generated pages, allowing us to do so also
without storing information about the portrait in the metadata pool.
Note: default is alias of https://gohugo.io/functions/compare/default/
