Add recursive watch

[0div]

Description

• WatchDir now performs a recursive directory traversal and watches recursively
• Some attention was given to specify which linux folders not to watch in the root folder (see comment for details)
• When a new directory is created, it is added to the watch list
• The WatchDirResponse now return absolute paths instead of relative paths to avoid confusions.
• nit: os.Lstat is used instead of os.Stat to avoid following symbolic links

Test

For now, the tests in js-sdk add some indirect coverage to this implementation

Side note on performance

• Lowered the number of default linux dirs being watched from ~4000 to ~800 with the regex filter.
• One call to WatchDir at the root did not increase goroutine count (usually 4)
• System performance in the container (TL;DR doesn't seem to affect it much)
  • without recursion:

  root@18bf07cd3f0f:/# uptime
  14:02:32 up 0 min,  0 user,  load average: 0.46, 0.10, 0.03
  
  top - 14:02:53 up 0 min,  0 user,  load average: 0.79, 0.20, 0.07
  Tasks:   3 total,   1 running,   2 sleeping,   0 stopped,   0 zombie
  %Cpu(s):  0.0 us,  0.1 sy,  0.0 ni, 99.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st 
  MiB Mem :  15974.8 total,  13557.3 free,   1055.5 used,   1594.0 buff/cache     
  MiB Swap:   1024.0 total,   1024.0 free,      0.0 used.  14919.3 avail Mem 

  • with recursion:

  root@18bf07cd3f0f:/# uptime
  14:03:15 up 1 min,  0 user,  load average: 0.95, 0.29, 0.10
  
  top - 14:03:37 up 1 min,  0 user,  load average: 1.02, 0.36, 0.13
  Tasks:   3 total,   1 running,   2 sleeping,   0 stopped,   0 zombie
  %Cpu(s):  0.0 us,  0.0 sy,  0.0 ni, 99.9 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st 
  MiB Mem :  15974.8 total,  13647.2 free,    960.4 used,   1602.5 buff/cache     
  MiB Swap:   1024.0 total,   1024.0 free,      0.0 used.  15014.4 avail Mem