abstract settings from codebase and replace with git-safe placeholders that don't match prod

[fool]

move node env vars and other settings out into a config file that won't be stored in git or anyway won't have values stored in git, cf https://shift2bikes.slack.com/archives/CCFLDTCF7/p1709920533388469?thread_ts=1709871971.848139&cid=CCFLDTCF7

I think @ionous is already working on this here: https://github.com/shift-org/shift-docs/pull/628

[ionous]

this is the list of env variables that need configuration for node ( only SHIFT_IMAGE_DIR is new; the rest were also needed for php ) -- along with the values that i think they had in production ( ??? for the ones i don't know. )

'MYSQL_HOST', 'db'
'MYSQL_USER', 'shift' 
'MYSQL_DATABASE', 'shift'
'MYSQL_PASSWORD', ????
'SMTP_HOST' ???
'SMTP_USER' ??? 
'SMTP_PASS' ??? 
'SHIFT_EMAIL_LOG', "/opt/node/shift-mail.log"
'SHIFT_IMAGE_DIR', "/opt/backend/eventimages" <-- new, but needed for node.
'SHIFT_DOMAIN', shift2bikes.org
'NGINX_HTTPS_PORT':443
'NGINX_HTTP_PORT':80