Changes

When the container is started, the original goaccess browsers.list (located in /goaccess/config/) is copied to the /goaccess-config directory. If the user defined the CUSTOM_BROWSERS variable with a comma delimited list consisting of Browser:Browser_category items, these are appended to the /goaccess-config/browsers.list file.
By checking if browsers.list is already present in the /goaccess-config directory at container runtime and subsequently removing it prior to copying over a fresh copy from the /goaccess/config directory, we can ensure that the browsers.list always aligns with the user's CUSTOM_BROWSERS variable. Since the /goaccess/config/browsers.list file is persistent, appending to it would result in custom browsers being left behind within the file when a user removes browser(s) from the CUSTOM_BROWSERS variable during a container restart - copying over a fresh file prior to appending custom browsers gets around this potential issue.
For user defined CUSTOM_BROWSERS, if a Browser has already been defined in browsers.list, it will be ignored and not appended to the list. Only the browser category (e.g., Crawlers) can be the same for multiple custom browser definitions.

If the ENABLE_BROWSERS_LIST variable is set to True, for each log type the corresponding goaccess.conf file has the line browsers-file /goaccess-config/browsers.list appended to it enabling the use of the browsers.list file.
If a user didn't define the CUSTOM_BROWSERS variable, this will still allow them to use the default goaccess browsers list. Note regarding Custom Log Types: Since a user may already have a browser.list file defined in their goaccess.conf file, if that is the case, their choice is respected instead of forcing them to use the file located at /goaccess-config/browsers.list. However, if they don't, but did enable the browsers list via the variable, then /goaccess-config/browsers.list is used and their custom browsers (if any defined) are appended to said file.

I went ahead and added documentation related to these two new variables to the README

xavier-hernandez / goaccess-for-nginxproxymanager