make: Update DB.make for markdown support

[landam]

This PR fixes #4740 (comment)

Note that links remain broken if GRASS is not built with specific driver support. See broken MySQL links in https://grass.osgeo.org/grass84/manuals/databaseintro.html#creating-a-database. This issue should be addressed by separated PR or at least reported as GitHub issue.

[neteler]

Thanks, it solves the problem (tested locally).

[neteler]

Seems we have a chicken-egg problem here (need to have the .md files in place to make the CI happy):

CI log:

make[3]: Entering directory '/home/runner/work/grass/grass/db/drivers'
make -C dbf || echo /home/runner/work/grass/grass/db/drivers/dbf >> /home/runner/work/grass/grass/error.log
make -C sqlite || echo /home/runner/work/grass/grass/db/drivers/sqlite >> /home/runner/work/grass/grass/error.log
make -C ogr || echo /home/runner/work/grass/grass/db/drivers/ogr >> /home/runner/work/grass/grass/error.log
make[4]: Entering directory '/home/runner/work/grass/grass/db/drivers/sqlite'
test -d OBJ.x86_64-pc-linux-gnu || mkdir -p OBJ.x86_64-pc-linux-gnu
make[4]: *** No rule to make target '/home/runner/work/grass/grass/dist.x86_64-pc-linux-gnu/docs/mkdocs/source/grass-sqlite.md', needed by 'db_html'.  Stop.
make[4]: *** Waiting for unfinished jobs....
make[4]: Entering directory '/home/runner/work/grass/grass/db/drivers/ogr'
test -d OBJ.x86_64-pc-linux-gnu || mkdir -p OBJ.x86_64-pc-linux-gnu
make[4]: Entering directory '/home/runner/work/grass/grass/db/drivers/dbf'
test -d OBJ.x86_64-pc-linux-gnu || mkdir -p OBJ.x86_64-pc-linux-gnu
make[4]: *** No rule to make target '/home/runner/work/grass/grass/dist.x86_64-pc-linux-gnu/docs/mkdocs/source/grass-ogr.md', needed by 'db_html'.  Stop.
make[4]: *** Waiting for unfinished jobs....
make[4]: Leaving directory '/home/runner/work/grass/grass/db/drivers/sqlite'
make[4]: *** No rule to make target '/home/runner/work/grass/grass/dist.x86_64-pc-linux-gnu/docs/mkdocs/source/grass-dbf.md', needed by 'db_html'.  Stop.
make[4]: *** Waiting for unfinished jobs....

[landam]

Seems we have a chicken-egg problem here (need to have the .md files in place to make the CI happy):

Yes, we have to comment it similarly as we did for other markdown-related rules: 6743f1a. They can be enabled in PR which adds markdown files.

[neteler]

Thanks!