Support msgmerge many POT files to update PO files

[truong-hua]

In gitflow or some other development flow, we usually have many separated environment and each environment will generate different .pot files. Current Weblate design requires us to do merging all .pot files of all environment to a single all.pot file externally. Besides, I don't think that having separated Weblate component per environment is a good way because it make translators operation more complicated.

Describe the solution you'd like

Support wildcard pattern for add-on Update PO files to match POT (msgmerge) and the add-on will do concatenating all .pot files by msgcat first (document suggest to use xgettext but I tried and it frequently crashes), and then doing msgmerge

Describe alternatives you've considered

Doing concatenating all pot files somewhere outside before pushing to Weblate.

Benefits

The configuration of Weblate for multi environment project will be easier and prevent mistaken from confliction of single pot file in different environments.

[keunes]

Maybe less relevant now that components/projects can be nested? #9731
(And, I think, addressing #11198 in one way or another could still improve this.)