Wire config.timeouts.tg_connect into UpstreamManager; per-attempt timeout uses
the same .max(1) pattern as connect_budget_ms.
Reject timeouts.tg_connect = 0 at config load (consistent with
general.upstream_connect_budget_ms and related checks). Default when the key
is omitted remains default_connect_timeout() via serde.
Fixestelemt/telemt#439
This commit adds support for configuring the data path via a
configuration file or command-line option. This may be useful
on systems without systemd, such as OpenWrt or Alpine Linux.
Signed-off-by: Maxim Anisimov <maxim.anisimov.ua@gmail.com>