Fix dependabot (#6986)

Follow-up to #6977 

Dependabot started failing after this because it was looking for all of
the relative includes that were inside of
`.github/project-root-duplicates/settings.gradle.kts`.

The solution that seems to work (I've tested on my fork) is to split
those includes out into a separate file, and `apply` that file.

Also fixes a busted markdown link (probably should have sent that in a
separate PR).

Resolves #6989

.github/project-root-duplicates/README.md → .github/dependabot-symlinks/README.md

@@ -1,5 +1,5 @@
 This directory and the two symlinks in it are used by the
-[dependabot configuration](../.github/dependabot.yml), because we can't include the root directory
+[dependabot configuration](../dependabot.yml), because we can't include the root directory
 in the dependabot scanning since then it will pick up all of the old library versions that we
 intentionally compile and test against.
 

.github/dependabot.yml

@@ -42,7 +42,7 @@ updates:
   - package-ecosystem: "gradle"
     # need to scope gradle dependency updates down in this repo because most of the instrumentations
     # intentionally test against old library versions
-    directory: ".github/project-root-duplicates"
+    directory: "/.github/dependabot-symlinks"
     rebase-strategy: "disabled"
     schedule:
       interval: "daily"

include-conventions.gradle.kts

@@ -0,0 +1,3 @@
+// this file is only split out from settings.gradle.kts due to a dependabot limitation
+// for details see .github/project-root-duplicates/README.md
+includeBuild("conventions")

settings.gradle.kts

@@ -84,7 +84,9 @@ buildCache {
 
 rootProject.name = "opentelemetry-java-instrumentation"
 
-includeBuild("conventions")
+// this is only split out due to a dependabot limitation
+// for details see .github/project-root-duplicates/README.md
+apply(from = "include-conventions.gradle.kts")
 
 include(":custom-checks")