feat(users/Profpatsch): add imap-idle r/2319

A small UCSPI client which connects to an IMAP server, authenticates
with username and password (for Christ’s sake, put it in
`s6-tlsclient`), selects the `INBOX` and proceeds to listen for new
mails.

Later it will generate an event on stdout and to be used for push
messaging and triggering a full `mbsync` run on new message.

Currently I’m testing it via

```
env CAFILE=/run/current-system/etc/ssl/certs/ca-bundle.crt \
  IMAP_USERNAME=<username> \
  backtick -i IMAP_PASSWORD ' pass' ' <password-entry>' '' \
  s6-tlsclient -v <imap-server> 993 ./result
```

Change-Id: I221717d374c0efc8d9e05fe0dfccba31798b3c5c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2636
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>

0 files changed, 0 insertions, 0 deletions