Add "--backup.mongodump.force_table_scan" option

[dschneller]

If set, this enables mongodump's --forceTableScan option which can speed up dumps significantly, especially when custom id fields are used or when the id values are large.

According to the discussion in TOOLS-845 this is safe to do for WiredTiger.

• https://jira.mongodb.org/browse/TOOLS-845?focusedCommentId=988298&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-988298
• https://jira.mongodb.org/browse/TOOLS-845?focusedCommentId=988414&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-988414

Defaults to false.

[timvaillancourt]

LGTM, thanks @dschneller