Ability to customize directory and permission behavior

[Presjar]

Hi,

Any chance to allow customization of the permissions setting during the container startup? I am using unraid and would like the Mask to be 000.

Also, when the docker auto restarts after a timeout of the vpn connection, the process of Setting permissions for download and incomplete directories and Setting permission for watch directory (775) and its files (664) cause my HDD to come out of sleep as these directory are flushed to from SSD to HDD once a week.

Perhaps we could have a configuration option to bypass the permission setting and also to set the desired umask?

From the logs:
`Enforcing ownership on transmission config directories
Applying permissions to transmission config directories
Setting owner for transmission paths to 99:100
Setting permissions for download and incomplete directories
Mask: 002
Directories: 775
Files: 664
Setting permission for watch directory (775) and its files (664)

---

Transmission will run as

User name: abc
User uid: 99
User gid: 100
-------------------------------------`