Rather than making the config dir world-readable, which potentially
leaks RPC credentials, the group of the directory is changed to the one
the service is executed as.
The phrasing seemed to indicate that the options specified in
ExecStart= could not be specified in the config file, necessitating
their inclusion in the service file. However, the options in the
config file simply get overridden by any specified in ExecStart=.
Tell systemd to create, set, and ensure the right mode for the PID,
configuration, and data directories.
Only the exec bit is set for groups for the aforementioned directories.
This is the least privilege perm that allows for the
reading/writing/execing of files under the directory _if_ the files
themselves give permission to its group to do so (e.g. when -sysperms is
specified). Note that this does not allow for the listing of files under
the directory.
Add comment how further options can be added or existing ones
modified. Use /run/${RuntimeDirectory} for PID file.
Remove TimeoutStopSec, TimeoutStartSec, StartLimitInterval,
StartLimitBurst directives as those should be set indivdually.
Remove Group to user the bitcoin user's default group.
Changed Restart from 'always' to 'on-failure' (can also be overwritten
individually).
