Support s3-compatible sinks

[eatonphil]

Companion PR in nimutils crashappsec/nimutils#98

sink_config chalk_s3_sink {
  enabled:  true
  sink:     "s3"
  endpoint: "http://localhost:8080"
  uri:      "s3://myorg/chalks3sink/report.json"
  uid:      "mykey"
  secret:   "mysecret"
  region:   "us-east-1"
}
subscribe("report", "my_rclone")

and to test

$ mkdir -p data/myorg
$ rclone serve s3 --auth-key "mykey,mysecret" data
$ ./chalk load s3sink.c4m
$ ./chalk insert ./chalk
$ ls data/myorg/chalks3sink
1777919291137-D00YFFGN2XG857EA5YG9Z1KJ5G-report.json

[miki725]

this pr needs to bump con4m with:

diff --git chalk.nimble chalk.nimble
index ba87089..20b69db 100644
--- chalk.nimble
+++ chalk.nimble
@@ -15,7 +15,7 @@ bin           = @["chalk"]

 # Dependencies
 requires "nim >= 2.0.8"
-requires "https://github.com/crashappsec/con4m#33743aada3a2db054804d92992d7df2536840012"
+requires "https://github.com/crashappsec/con4m#e8020aa2768041ee760739df96494d26d84ed8d2"
 requires "https://github.com/viega/zippy == 0.10.7" # MIT
 requires "https://github.com/NimParsers/parsetoml == 0.7.1" # MIT

[eatonphil]

Closing in favor of #663.