DOC: http: rename the unique-id sample and add the documentation

This patch renames the ssample fetch from "uniqueid" to "unique-id".
It also adds the documentation associated with this sample fetch.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 6b80158..9798f32 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -13900,6 +13900,14 @@
   example, 302. It is mostly used within ACLs and integer ranges, for example,
   to remove any Location header if the response is not a 3xx.
 
+unique-id : string
+  Returns the unique-id attached to the request. The directive
+  "unique-id-format" must be set. If it is not set, the unique-id sample fetch
+  fails. Note that the unique-id is usually used with HTTP requests, however this
+  sample fetch can be used with other protocols. Obviously, if it is used with
+  other protocols than HTTP, the unique-id-format directive must not contain
+  HTTP parts. See: unique-id-format and unique-id-header
+
 url : string
   This extracts the request's URL as presented in the request. A typical use is
   with prefetch-capable caches, and with portals which need to aggregate
diff --git a/src/proto_http.c b/src/proto_http.c
index 6ab14ce..82d4b87 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -12817,7 +12817,7 @@
 	{ "shdr_val",        smp_fetch_hdr_val,        ARG2(0,STR,SINT), val_hdr, SMP_T_SINT, SMP_USE_HRSHV },
 
 	{ "status",          smp_fetch_stcode,         0,                NULL,    SMP_T_SINT, SMP_USE_HRSHP },
-	{ "uniqueid",        smp_fetch_uniqueid,       0,                NULL,    SMP_T_STR,  SMP_SRC_L4SRV },
+	{ "unique-id",       smp_fetch_uniqueid,       0,                NULL,    SMP_T_STR,  SMP_SRC_L4SRV },
 	{ "url",             smp_fetch_url,            0,                NULL,    SMP_T_STR,  SMP_USE_HRQHV },
 	{ "url32",           smp_fetch_url32,          0,                NULL,    SMP_T_SINT, SMP_USE_HRQHV },
 	{ "url32+src",       smp_fetch_url32_src,      0,                NULL,    SMP_T_BIN,  SMP_USE_HRQHV },