journal-remote: small fixes
journal-remote: reject fields above maximum size

Also fix an infinite loop on E2BIG.

Remember what range we already scanned for '\n', to avoid
quadratic behaviour on long "text" fields.
journal-upload: a tool to push messages to systemd-journal-remote
journal-upload: HTTPS support
journal-upload: use journal as the source
journal-upload: make state persistent
journal-upload: add watchdog support
journal-remote: add units and read certs from default locations
shared/socket-util: add function to query remote address
shared/socket-label: fix error message

Was: Failed to listen on [::]:2000: Success
Add simple generator of fake journal export stream
Allow addresses to be specified for --listen-... args

Hostnames still aren't accepted.
journal-remote: allow splitting incoming logs by source host

Previously existing scheme where the file name would be based on
the source was just too ugly and unpredicatable. Now there are
only two options:
  1. just one file (until rotation),
  2. one file per source host, using the hostname as filename part.
For the cases where the source is specified by the user, only
option one is allowed, and the full of the file must be specified.
Constify ConfigTableItem tables
Fix problem with allocating large buffers and log leftovers
journal-remote: improve some messages
journal-remote: rework fd and writer reference handling
journal-remote: let user specify just the main part of the url

We can append /upload ourselves.
journal-upload: add config file
man: document systemd-journal-upload