chore: group dependabot updates, bump posthog-rs, clean up deny.toml (#434)

Author: grandizzy

.changelog/dependabot-grouping-posthog-bump.md

@@ -0,0 +1,5 @@
+---
+tempo-common: patch
+---
+
+Bump posthog-rs 0.5.0 → 0.5.3 (drops reqwest 0.11/rustls 0.21 chain), remove stale advisory ignores, add dependabot update grouping.

.github/dependabot.yml

@@ -7,6 +7,11 @@ updates:
     open-pull-requests-limit: 10
     cooldown:
       default-days: 7
+    groups:
+      cargo-weekly:
+        applies-to: "version-updates"
+        patterns: ["*"]
+        update-types: ["minor", "patch"]
 
   - package-ecosystem: "github-actions"
     directory: "/"
@@ -15,3 +20,8 @@ updates:
     open-pull-requests-limit: 10
     cooldown:
       default-days: 7
+    groups:
+      actions-weekly:
+        applies-to: "version-updates"
+        patterns: ["*"]
+        update-types: ["minor", "patch"]