fix: fix release-please PR title pattern and permissions (#1978)

## Summary

- Add `group-pull-request-title-pattern` with `${version}` so
  release-please can match the merged PR and create the GitHub release.
  The default group title is `chore: release main` which lacks the
  version, preventing release creation on merge.
- Add `issues: write` permission (incorporates #1975)
- Remove `separate-pull-requests: false` (already the default)
- Remove redundant `extra-files` (maven type auto-discovers pom.xml)

Supersedes #1975

## Test plan

- [ ] CI passes
- [ ] After merge, release-please creates PR with title like
  `chore(main): release 1.5.1`
- [ ] Merging that PR creates v1.5.1 tag and GitHub release

Signed-off-by: Gregor Zeitlinger <gregor.zeitlinger@grafana.com>

Author: zeitlinger

.github/config/release-please-config.json

@@ -1,11 +1,10 @@
 {
   "$schema": "https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json",
-  "separate-pull-requests": false,
+  "group-pull-request-title-pattern": "chore${scope}: release${component} ${version}",
   "pull-request-footer": "> [!IMPORTANT]\n> Close and reopen this PR to trigger CI checks.",
   "packages": {
     ".": {
-      "release-type": "maven",
-      "extra-files": ["integration-tests/it-spring-boot-smoke-test/pom.xml"]
+      "release-type": "maven"
     }
   }
 }

.github/workflows/release-please.yml

@@ -8,6 +8,7 @@ on:
 
 permissions:
   contents: write
+  issues: write
   pull-requests: write
 
 jobs: