Set proper default values for core settings.

If nothing set in the settings file some entries need to be default set:
COMPRESSION
COMPRESSION_LEVEL
ENCRYPTION
FORCE_CHECK
KEEP_LAST
KEEP_HOURS
KEEP_DAYS
KEEP_WEEKS
KEEP_MONTHS
KEEP_YEARS

If these variables are empty after settings file is ready they are set
to the default value. After that the sub configs override those settings

Readme.md

@@ -35,6 +35,18 @@ eg:
 
 If `FILE_REPOSITORY_COMPATIBLE` is set to `false` in the borg.backup.file.settings then the file borg name will have `-file` added too. Currently this is not added to stay compatible with older scripts
 
+All below have default values if not set in the main settings file
+ * COMPRESSION: zstd
+ * COMPRESSION_LEVEL: 3
+ * ENCRYPTION: none
+ * FORCE_CHECK: false
+ * KEEP_LAST: 0
+ * KEEP_HOURS: 0
+ * KEEP_DAYS: 7
+ * KEEP_WEEKS: 4
+ * KEEP_MONTHS: 6
+ * KEEP_YEARS: 1
+
 All module settings files can have the following prefixed with `SUB_` to override master settings:
  * SUB_BACKUP_FILE
  * SUB_COMPRESSION