Revise translation html to be chunked

[robe]

We changed out default build html to be chunked from single file.

Darafei pointed out that google doesn't index the translations too well because they are a single. Not to mention they are harder to use online.

So we should revise to chunking these like we have the english one. So instead of ​https://postgis.net/docs/manual-dev/postgis-ja.html

We'd have a subfolder - ​https://postgis.net/docs/manual-dev/postgis-ja

with same files as what is in main folder, but for japanese translation. And so on.

We could actually keep both I guess since the translation as a single file is easier to download, but for indexing goodness better as separate files per function/help section.