use ENV variables instead of hardcoded values

mysql.dockerfile

@@ -1,8 +1,19 @@
 FROM mysql:5.7
 
-ENV MYSQL_ROOT_PASSWORD=root \
-    MYSQL_DATABASE=wordpress \
-    MYSQL_USER=wp_admin \
-    MYSQL_PASSWORD=wp_password
+ARG API_URL
 
-ADD database/clean-dump.sql /docker-entrypoint-initdb.d/dump.sql
+ARG MYSQL_ROOT_PASSWORD 
+ARG MYSQL_DATABASE 
+ARG MYSQL_USER
+ARG MYSQL_PASSWORD
+
+ENV API_URL ${API_URL}
+
+ENV MYSQL_ROOT_PASSWORD ${MYSQL_ROOT_PASSWORD}
+ENV MYSQL_DATABASE ${MYSQL_DATABASE}
+ENV MYSQL_USER ${MYSQL_USER}
+ENV MYSQL_PASSWORD ${MYSQL_PASSWORD}
+
+
+ADD database/clean-dump.sql /home/dump.sql
+RUN sed -i -e 's@API_URL_PLACEHOLDER@'$API_URL'@g' /home/dump.sql && cp /home/dump.sql /docker-entrypoint-initdb.d