asterisk: 24.0.0-rc2 image built from source with static config

Adds stub configs and noloads so a clean boot logs no ERROR lines,
ships stock indications.conf, seeds default MOH from the entrypoint.
Spec 01 synced with the real files.

Task: M0-T5

asterisk/conf/extensions.conf

@@ -0,0 +1,11 @@
+[general]
+static = yes
+writeprotect = yes
+clearglobalvars = yes
+
+[globals]
+#include selfphoneng/extensions_globals_selfphoneng.conf
+
+; Static helper contexts (sp-sub-*) are generated too (03 §5) so that all
+; dialplan lives in one place in code.
+#include selfphoneng/extensions_selfphoneng.conf