RFR: 6203: Add ZGC allocation stall rule

[Suchita Chaturvedi]

This enhancement is to add new rule for ZGC Allocation Stall events.

The default configuration:
 
<img width="946" alt="image" src="https://github.com/user-attachments/assets/0d39ae26-fdc4-49e3-a0ed-fb7f7da8f709" />

Here are few screenshots for reference:

<img width="344" alt="image" src="https://github.com/user-attachments/assets/e7efe1e2-d6b3-4a05-8ea6-1bf2e8b8c15f" />

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Commit messages:
 - 6203: Add ZGC allocation stall rule

Changes: https://git.openjdk.org/jmc/pull/664/files
  Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=664&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-6203
  Stats: 307 lines in 11 files changed: 303 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jmc/pull/664.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/664/head:pull/664

PR: https://git.openjdk.org/jmc/pull/664