Refactor scan mailbox form and add flag for post-processing

Mails are filtered once by using an imap search and then by some globs
to filter files and subjects. Imap can search by subject via a
string-contains, but not via globs or patterns (afaik). The subject
filter is applied to all downloaded mail headers. Now for post
processing (moving to some target folder or deleting), it can be
chosen to post-process all "seen" mails or only those that matched all
filters.

modules/restapi/src/main/resources/docspell-openapi.yml

@@ -3904,6 +3904,8 @@ components:
             processing mails.
           type: string
           format: language
+        postHandleAll:
+          type: boolean
 
     ImapSettingsList:
       description: |