config: add VERSION_FIRMWARE_URL

This new value points to where firmware can be downloaded. It's not
about a single release but all available firmware releases.

In the next step, this URL should be exposed via `ubus call system
board` as an entry of the `distribution` field. With that value, the
running firmware can check for newer releases.

We already have VERSION_REPO however that's different and only meant for
package managers to download their fitting package indexes/packages.

Signed-off-by: Paul Spooren <mail@aparcar.org>
Link: https://github.com/openwrt/openwrt/pull/17780
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

package/base-files/files/usr/lib/os-release

@@ -7,6 +7,7 @@ VERSION_ID="%v"
 HOME_URL="%u"
 BUG_URL="%b"
 SUPPORT_URL="%s"
+FIRMWARE_URL="%f"
 BUILD_ID="%R"
 OPENWRT_BOARD="%S"
 OPENWRT_ARCH="%A"

package/base-files/image-config.in

@@ -241,6 +241,12 @@ if VERSIONOPT
 		help
 			This an URL to provide users seeking support
 
+	config VERSION_FIRMWARE_URL
+		string
+		prompt "Firmware URL"
+		help
+			This is an URL to provide users for downloading firmware
+
 	config VERSION_PRODUCT
 		string
 		prompt "Product name"