bitbake: bitbake: registry: make a separate configuration for poky with sstate mirror

Using sstate mirror places much higher requirements on both network robustness
and network bandwidth than just fetching source code. When the network doesn't meet
those, the user experience can be very frustrating as errors can be cryptic and
intermittent, or bitbake would just seemingly do nothing for a long time.

Let's make sstate an opt-in, and provide a caution for using it. When it does
work, it works wonderfully and does accelerate builds significantly.

(Bitbake rev: fe88a8e9cd5ccbc26508cf524a2f71a06d3df03a)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/default-registry/configurations/poky-master.conf.json

@@ -53,10 +53,7 @@
     "bitbake-setup": {
         "configurations": [
         {
-            "name": "poky",
-            "description": "Poky - The Yocto Project testing distribution",
             "bb-layers": ["openembedded-core/meta","meta-yocto/meta-yocto-bsp","meta-yocto/meta-poky"],
-            "oe-fragments": ["core/yocto/sstate-mirror-cdn"],
             "oe-fragments-one-of": {
                 "machine": {
                     "description": "Target machines",
@@ -66,7 +63,18 @@
                     "description": "Distribution configuration variants",
                     "options" : ["distro/poky", "distro/poky-altcfg", "distro/poky-tiny"]
                 }
+            },
+            "configurations": [
+            {
+                "name": "poky",
+                "description": "Poky - The Yocto Project testing distribution"
+            },
+            {
+                "name": "poky-with-sstate",
+                "description": "Poky - The Yocto Project testing distribution with internet sstate acceleration. Use with caution as it requires a completely robust local network with sufficient bandwidth.",
+                "oe-fragments": ["core/yocto/sstate-mirror-cdn"]
             }
+            ]
         }
         ]
     },