Issues with uid_tracking marking emails as read

[pemontto]

There are some issues with the new uid_tracking option. I expect the most common use for this config is so a mailbox can be used by normal users without this logstash-input-imap changing the state of messages.

Some issues currently:

• Emails are always marked as READ (interrupts normal usage)
• Inboxes with no UNSEEN/NOT SEEN messages aren't scanned if uid_tracking is on and there is no uid_last_value. E.g. using it on a Sent mailbox will produce no results as everything is already "SEEN"

I'm proposing a new flag mark_read which will default to true (maintaining current behaviour), but when enabled with uid_tracking will not change the email FLAGS.

[mikehwang]

Why have these PRs been not reviewed?