RFR: 8308475: Make the thread dump files generated by jcmd Thread.dump_to_file jtreg failure handler action easily accessible

[Jaikiran Pai]

Can I please get a review of this change which proposes to improve the accessibility of the thread dump files that are generated by the `jcmd Thread.dump_to_file` command configured in the failure handler configurations? This addresses https://bugs.openjdk.org/browse/JDK-8308475. 

The changes in this PR include:
 - Enhancement to `GatherProcessInfoTimeoutHandler` to allow configuring a `successArtifacts` action parameter which can be used to generate links to files that are generated by the failure handler commands.
 - Introduction of a `%iterCount` token to allow ability to refer to the current iteration when the command is repeated
 - The `jcmd Thread.dump_to_file` is now configured to create the thread dumps in `json` format. Additionally, it has now been configured to create the thread dumps 6 times, just like the `jstack` command.

Detailed explanation of the `successArtifacts` parameter and the `%iterCount` token is provided in the JBS comment here https://bugs.openjdk.org/browse/JDK-8308475?focusedCommentId=14583072&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14583072

Tests have been run locally with this change and tier1, tier2 and tier3 tests on CI system to verify this change works and doesn't cause regression.

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Commit messages:
 - 8308475: Make the thread dump files generated by jcmd Thread.dump_to_file jtreg failure handler action easily accessible

Changes: https://git.openjdk.org/jdk/pull/14071/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14071&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308475
  Stats: 78 lines in 5 files changed: 66 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/14071.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14071/head:pull/14071

PR: https://git.openjdk.org/jdk/pull/14071