check_alloy: Rewrite to auto-discover all supported components and report drops

[konstantinbest]

Example output:

OK - 3 component(s) checked | loki_write_default_dropped=0.0;10485760.0;52428800.0;0 loki_write_default_sent=9356.0 prometheus_remote_write_mimir_dropped=0.0;10485760.0;52428800.0;0 prometheus_remote_write_mimir_sent=4000.0 pyroscope_write_default_dropped=0.0;10485760.0;52428800.0;0 pyroscope_write_default_sent=0.0
Component                      Status  Dropped    Sent
-----------------------------  ------  ---------  ------------
loki.write.default             OK      0 bytes    9356 bytes
prometheus.remote_write.mimir  OK      0 samples  4000 samples
pyroscope.write.default        OK      0 bytes    0 bytes

[Phantuman]

LGTM