Promtail Syslog UDP transport

[ldb]

Is your feature request related to a problem? Please describe.
When using Promtail with Syslog we would like to use UDP transport to prevent promtail from becoming a potential bottleneck for syslog. Implementing UDP transport would help us with that.

Describe the solution you'd like
We would like to see UDP transport being supported by the promtail syslog receiver.

Describe alternatives you've considered
Keep using the TCP receiver. Alternatively, we could also think about unix socket transport, so that forwarding on localhost is even faster.

Additional context
None.