lib/config: add environment variable to set config file

Previously it was assumed that `config.json` would be placed in
the same directory as the rest of CodiMD without any optional override.

This allows to override the path to the `config.json` by setting
`CMD_CONFIG_FILE` to the canonical path of the desired config file.

Signed-off-by: WilliButz <wbutz@cyberfnord.de>

lib/config/index.js

@@ -23,7 +23,8 @@ const packageConfig = {
   minimumCompatibleVersion: '0.5.0'
 }
 
-const configFilePath = path.join(appRootPath, 'config.json')
+const configFilePath = path.resolve(appRootPath, process.env.CMD_CONFIG_FILE ||
+'config.json')
 const fileConfig = fs.existsSync(configFilePath) ? require(configFilePath)[env] : undefined
 
 let config = require('./default')