Move scripts used in CI to the new location (#5198)

* Move CI scripts and update references

* Update paths in .gitlab-ci.yml

* Removed outdated entries from CODEOWNERS

polkadot/scripts/ci/changelog/templates/global_priority.md.tera

@@ -0,0 +1,29 @@
+{% import "high_priority.md.tera" as m_p -%}
+## Upgrade Priority
+
+{%- set polkadot_prio = 0 -%}
+{%- set substrate_prio = 0 -%}
+
+{# We fetch the various priorities #}
+{%- if polkadot.meta.C -%}
+    {%- set polkadot_prio = polkadot.meta.C.max -%}
+{%- endif -%}
+{%- if substrate.meta.C -%}
+    {%- set substrate_prio = substrate.meta.C.max -%}
+{%- endif -%}
+
+{# We compute the global priority #}
+{%- set global_prio = polkadot_prio -%}
+{%- if substrate_prio > global_prio -%}
+    {%- set global_prio = substrate_prio -%}
+{%- endif -%}
+
+{# We show the result #}
+{{ m_p::high_priority(p=global_prio, changes=changes) }}
+
+<!--
+- Polkadot: {{ polkadot_prio }}
+- Substrate: {{ substrate_prio }}
+-->
+
+{# todo: show high prio list here #}