Create strict mode for interpretation of Lua config #2381

osm2pgsql doesn't check for settings it doesn't know about so that we can introduce them later without old versions of osm2pgsql breaking. But maybe we should at least check and print a warning? And then have a mechanism that turns those warnings into errors for tests?

This affects all sorts of configurations where we use Lua tables with config settings. In each of these cases we would need to keep a list of allowed "keys" and check all "values".

Options:

• Have a command line option "--strict" or similar
• Have an environment variable "OSM2PGSQL_STRICT" or similar
• Have an option osm2pgsql.strict_mode=true or similar in the Lua config file

Do we expect users to use this strict mode also or is this just for tests?