Use LDFLAGS to set the default locations in docker

Too many docker users are caught out by the default location for the
app.ini file being environment dependent so that when they docker exec
into the container the `gitea` commands do not work properly and require
additional `-c` arguments to correctly pick up the configuration.

This PR simply builds the default locations into the build.

Fix go-gitea#14468
Reference go-gitea#17497
Reference go-gitea#12082
Reference go-gitea#8941
 ... amongst others ...

Signed-off-by: Andrew Thornton <art27@cantab.net>

Dockerfile

@@ -9,6 +9,8 @@ ENV GOPROXY ${GOPROXY:-direct}
 ARG GITEA_VERSION
 ARG TAGS="sqlite sqlite_unlock_notify"
 ENV TAGS "bindata timetzdata $TAGS"
+ENV LDFLAGS="$LDFLAGS -X \"code.gitea.io/gitea/modules/setting.CustomPath=/data/gitea\" \
+  -X \"code.gitea.io/gitea/modules/setting.AppWorkPath=/app/gitea\""
 ARG CGO_EXTRA_CFLAGS
 
 #Build deps

Dockerfile.rootless

@@ -9,6 +9,9 @@ ENV GOPROXY ${GOPROXY:-direct}
 ARG GITEA_VERSION
 ARG TAGS="sqlite sqlite_unlock_notify"
 ENV TAGS "bindata timetzdata $TAGS"
+ENV LDFLAGS="$LDFLAGS -X \"code.gitea.io/gitea/modules/setting.CustomPath=/var/lib/gitea/custom\" \
+  -X \"code.gitea.io/gitea/modules/setting.CustomConf=/etc/gitea/conf.ini\" \
+  -X \"code.gitea.io/gitea/modules/setting.AppWorkPath=/var/lib/gitea\""
 ARG CGO_EXTRA_CFLAGS
 
 #Build deps