s3 backend: optional HTTP client settings for the cloud tier (#11897)

* s3 backend: optional HTTP client settings for the cloud tier

The S3 tier backend builds its client from a bare aws.Config, so it always
uses Go's default transport: HTTP/2 wherever the endpoint offers it over TLS,
no cap on connections per host, and a 90s idle timeout. Against some
S3-compatible services that is a poor fit. Over HTTP/2 every upload and
range read of a tiered volume shares one connection and its flow-control
window; with a small window, tier uploads and concurrent reads of tiered
volumes become throughput-bound on that one connection, while HTTP/1.1 opens
a connection per concurrent request. Some services also limit parallel
connections per client address, or drop idle connections before 90s.

Add three optional settings to [storage.backend.s3.<id>], all off by
default so existing deployments keep the SDK's default client:
- disable_http2: keep the client on HTTP/1.1 (ForceAttemptHTTP2=false and an
  empty TLSNextProto, the documented opt-out);
- max_connections: MaxConnsPerHost, 0 = no cap;
- idle_connection_timeout_seconds: IdleConnTimeout, 0 = Go's default.

The session cache key includes the options when any is set, so two backends
on the same endpoint with different settings do not share a client.
ToProperties reports the settings; the master.toml scaffold documents them.

Tests: TestS3BackendHTTPOptionsReachTheClient fails without the change (the
settings never reach the client); TestS3BackendDefaultHTTPClientUnchanged,
TestS3BackendSessionsDifferByHTTPOptions, TestParseNonNegative.

* s3 backend: reject an idle timeout too large for time.Duration

An idle_connection_timeout_seconds above math.MaxInt64/1e9 overflowed when
multiplied by time.Second. The negative result made the transport keep its
default timeout and ToProperties export a negative value. Warn and use the
default instead.

* s3 backend: parse the idle timeout as 64-bit seconds

parseIdleConnTimeout went through strconv.Atoi, so on 32-bit platforms
any value above 2147483647 seconds was rejected while the same value was
accepted on 64-bit, and the overflow test failed under GOARCH=386. Parse
with ParseInt(…, 64) and export the effective value with FormatInt so the
accepted range is the same on every platform.

---------

Co-authored-by: Javier de la Torre <jatorre@lakehousebox.com>

weed/command/scaffold/master.toml

@@ -28,6 +28,10 @@ region = "us-east-2"
 bucket = "your_bucket_name"    # an existing bucket
 endpoint = ""
 storage_class = "STANDARD_IA"
+# optional HTTP client tuning for S3-compatible services:
+# disable_http2 = false                 # true keeps the client on HTTP/1.1, one connection per concurrent request
+# max_connections = 0                   # cap on connections to the endpoint, 0 = no cap
+# idle_connection_timeout_seconds = 0   # close idle connections sooner, 0 = Go default (90s)
 
 # create this number of logical volumes if no more writable volumes
 # count_x means how many copies of data.