s3: add Pure Storage FlashBlade provider support (#8575)

Pure Storage FlashBlade is an enterprise object storage platform that
provides S3-compatible APIs. This change adds FlashBlade as a new
provider option in the S3 backend.

Before this change, FlashBlade users had to use the "Other" provider
with manual configuration of various compatibility flags. This often
resulted in suboptimal performance due to conservative default settings.

After this change, users can select the "FlashBlade" S3 provider and
get an optimal configuration:

- ListObjectsV2 enabled for better performance
- AWS-compatible multipart ETags for reliable transfers
- Proper handling of "AlreadyOwnedByYou" bucket creation responses
- Path-style URLs by default (virtual-host style with DNS setup)
- Unsigned payloads to ensure compatibility with all rclone features

FlashBlade supports modern S3 features including trailer checksum
algorithms (SHA256, CRC32, CRC32C), object versioning, and lifecycle
management.

Provider settings were verified by testing against a FlashBlade//E
system running Purity//FB 4.5.7.

Documentation and test configurations are included.

Integration test results:
```
go test -v -fast-list -remote TestS3FlashBlade:
PASS
ok  	github.com/rclone/rclone/backend/s3	232.444s
```

backend/s3/s3.go

@@ -101,6 +101,9 @@ var providerOption = fs.Option{
 	}, {
 		Value: "Dreamhost",
 		Help:  "Dreamhost DreamObjects",
+	}, {
+		Value: "FlashBlade",
+		Help:  "Pure Storage FlashBlade Object Storage",
 	}, {
 		Value: "GCS",
 		Help:  "Google Cloud Storage",
@@ -567,7 +570,7 @@ func init() {
 		}, {
 			Name:     "region",
 			Help:     "Region to connect to.\n\nLeave blank if you are using an S3 clone and you don't have a region.",
-			Provider: "!AWS,Alibaba,ArvanCloud,ChinaMobile,Cloudflare,IONOS,Petabox,Liara,Linode,Magalu,Qiniu,RackCorp,Scaleway,Selectel,Storj,Synology,TencentCOS,HuaweiOBS,IDrive",
+			Provider: "!AWS,Alibaba,ArvanCloud,ChinaMobile,Cloudflare,FlashBlade,IONOS,Petabox,Liara,Linode,Magalu,Qiniu,RackCorp,Scaleway,Selectel,Storj,Synology,TencentCOS,HuaweiOBS,IDrive",
 			Examples: []fs.OptionExample{{
 				Value: "",
 				Help:  "Use this if unsure.\nWill use v4 signatures and an empty region.",
@@ -1908,7 +1911,7 @@ func init() {
 		}, {
 			Name:     "location_constraint",
 			Help:     "Location constraint - must be set to match the Region.\n\nLeave blank if not sure. Used when creating buckets only.",
-			Provider: "!AWS,Alibaba,ArvanCloud,HuaweiOBS,ChinaMobile,Cloudflare,IBMCOS,IDrive,IONOS,Leviia,Liara,Linode,Magalu,Outscale,Qiniu,RackCorp,Scaleway,Selectel,StackPath,Storj,TencentCOS,Petabox",
+			Provider: "!AWS,Alibaba,ArvanCloud,HuaweiOBS,ChinaMobile,Cloudflare,FlashBlade,IBMCOS,IDrive,IONOS,Leviia,Liara,Linode,Magalu,Outscale,Qiniu,RackCorp,Scaleway,Selectel,StackPath,Storj,TencentCOS,Petabox",
 		}, {
 			Name: "acl",
 			Help: `Canned ACL used when creating buckets and storing or copying objects.
@@ -1923,7 +1926,7 @@ doesn't copy the ACL from the source but rather writes a fresh one.
 If the acl is an empty string then no X-Amz-Acl: header is added and
 the default (private) will be used.
 `,
-			Provider: "!Storj,Selectel,Synology,Cloudflare",
+			Provider: "!Storj,Selectel,Synology,Cloudflare,FlashBlade",
 			Examples: []fs.OptionExample{{
 				Value:    "default",
 				Help:     "Owner gets Full_CONTROL.\nNo one else has access rights (default).",
@@ -1981,6 +1984,7 @@ isn't set then "acl" is used instead.
 If the "acl" and "bucket_acl" are empty strings then no X-Amz-Acl:
 header is added and the default (private) will be used.
 `,
+			Provider: "!Storj,Selectel,Synology,Cloudflare,FlashBlade",
 			Advanced: true,
 			Examples: []fs.OptionExample{{
 				Value: "private",
@@ -3495,6 +3499,9 @@ func setQuirks(opt *Options) {
 	case "Dreamhost":
 		urlEncodeListings = false
 		useAlreadyExists = false // untested
+	case "FlashBlade":
+		mightGzip = false        // Never auto gzips objects
+		virtualHostStyle = false // supports vhost but defaults to paths
 	case "IBMCOS":
 		listObjectsV2 = false // untested
 		virtualHostStyle = false