[SSSD] [sssd PR#596][opened] [CONFDB]:[RFE] Add "enabled" option to domain section

[amitkumar50]

   URL: https://github.com/SSSD/sssd/pull/596
Author: amitkumar50
 Title: #596: [CONFDB]:[RFE] Add "enabled" option to domain section
Action: opened

PR body:
"""
Upstream Request:
Instead of enabling domains using the "domains" option in [sssd]
section we could have [domain/*] option "enabled". This would allow
admins to configure and enable domain in the same snippet file.

This Fix would be submitted in 2 patches:
Patch-1(This Patch):
- Introduces 'enabled' option in domain section
- Introduces 'CONFDB_DOMAIN_ENABLED' variable to retrieve enabled value
from confdb
- Code to call start_service() routine only for domains having enabled=1

Patch-2(Upcoming):
- Would remove 'domains' option from sssd section.
- Would remove corresponding code to parse 'domains' option
- Providing a check that atlest One domain have enabled option set.

Resolves: https://pagure.io/SSSD/sssd/issue/3735
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/596/head:pr596
git checkout pr596