The `xactfetch` script now uses a helper tool, `secretsocket` to
handle looking up secrets. This tool supports various secret source
types, including files, environment variables, and external commands.
Separating this functionality out of the main script makes it a lot
more flexible and pluggable. It's main purpose, though, was actually
to allow `xactfetch` to run in a container while communicating with
`rbw` outside that container, specifically for development puposes.
The `secretsocket` tool reads its configuration from a TOML document.
This document defines the secrets the tool handles, and how to look
them up.
Note that the `xactfetch` container image no longer defines the
`XDG_CONFIG_HOME` environment variable, as it uses Chromium instead of
Firefox now, and the former does not work with a read-only config
directory. As such, we have to mount the `rbw` configuration in the
default location.