add junos_system_syslog_user resource

[jeremmfr]

FEATURES:

• add junos_system_syslog_user resource (Fix Feature request: junos_system_syslog_user #593)

ENHANCEMENTS:

• resource/junos_system_syslog_file: resource now use new terraform-plugin-framework
  some of config errors are now sent during Plan instead of during Apply
  optional boolean attributes doesn't accept value false
  optional string attributes doesn't accept empty value
  the resource schema has been upgraded to have one-blocks in single mode instead of list
• resource/junos_system_syslog_host: resource now use new terraform-plugin-framework
  optional boolean attributes doesn't accept value false
  optional string attributes doesn't accept empty value
  the resource schema has been upgraded to have one-blocks in single mode instead of list

BUG FIXES:

• resource/junos_system_syslog_file: fix reading archive size when value is a multiple of 1024 (k,m,g)