feat: Allow jobs to spawn detached (#312)

Add the field `detached` to the job object to allow for spawning jobs in
a detached state. This passes `options.spawned` to `uv.spawn` which
causes the child process to become a process group leader allowing it to
persist after the parent process exits.

Author: erooke

lua/plenary/job.lua

@@ -16,6 +16,7 @@ local F = require "plenary.functional"
 ---@field on_exit function        : (self, code: number, signal: number)
 ---@field maximum_results number  : stop processing results after this number
 ---@field writer Job|table|string : Job that writes to stdin of this job.
+---@field detached boolean        : Spawn the child in a detached state making it a process group leader
 ---@field enabled_recording boolean
 local Job = {}
 Job.__index = Job
@@ -131,6 +132,10 @@ function Job:new(o)
     obj.interactive = o.interactive
   end
 
+  if o.detached then
+    obj.detached = true
+  end
+
   -- enable_handlers: Do you want to do ANYTHING with the stdout/stderr of the proc
   obj.enable_handlers = F.if_nil(o.enable_handlers, true, o.enable_handlers)
 
@@ -272,6 +277,10 @@ function Job:_create_uv_options()
     options.env = self.env
   end
 
+  if self.detached then
+    options.detached = true
+  end
+
   return options
 end