[8.14] ci(release-minor): add apm- prefix and create release diff between patches (backport #13065)

[mergify]

Motivation/summary

Support release automation for FF with:

• adding apm- prefix to Asciidoc links and targets
• using tags instead of branches in compare links

Test

$  make rename-changelog RELEASE_BRANCH=8.15 RELEASE_VERSION=8.15.0 VERSION=8.15
>> common-changelog
>> rename-changelog

produced:

diff --git a/CHANGELOG.asciidoc b/CHANGELOG.asciidoc
index 623bc75af..dffd289c9 100644
--- a/CHANGELOG.asciidoc
+++ b/CHANGELOG.asciidoc
@@ -1,4 +1,5 @@
 // tag::list[]
+* <<apm-release-notes-8.15>>
 * <<apm-release-notes-8.14>>
 * <<apm-release-notes-8.13>>
 * <<apm-release-notes-8.12>>
@@ -18,6 +19,7 @@
 
 // tag::includes[]
 include::./changelogs/head.asciidoc[]
+include::./changelogs/8.15.asciidoc[]
 include::./changelogs/8.14.asciidoc[]
 include::./changelogs/8.13.asciidoc[]
 include::./changelogs/8.12.asciidoc[]
diff --git a/changelogs/head.asciidoc b/changelogs/head.asciidoc
index a3cf1bf26..52107f228 100644
--- a/changelogs/head.asciidoc
+++ b/changelogs/head.asciidoc
@@ -1,7 +1,7 @@
 [[release-notes-head]]
 == APM version HEAD
 
-https://github.com/elastic/apm-server/compare/8.14\...main[View commits]
+https://github.com/elastic/apm-server/compare/8.15\...main[View commits]
 
 [float]
 ==== Breaking Changes

and

[[apm-release-notes-8.15]]
== APM version 8.15
* <<apm-release-notes-8.15.0>>

[float]
[[apm-release-notes-8.15.0]]
=== APM version 8.15.0

https://github.com/elastic/apm-server/compare/v8.13.2\...v8.15.0[View commits]

[float]
==== Breaking Changes

[float]
==== Deprecations

[float]
==== Intake API Changes

[float]
==== Added

Checklist

• Update CHANGELOG.asciidoc
• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

Related issues

Behaviour changed in #12820

Part of #12989

---

This is an automatic backport of pull request #13065 done by [Mergify](https://mergify.com).