Add looped mode support for bulk ingestion operation.

[rishabh6788]

Description

This PR added looped mode parameter for bulk operations. Using this users will be able run ingestion even when the corpus is not big enough to sustain long term indexing at any specified rate.

If not time-period is defined and looped mode is set to true then ingestion would run indefinitely.

Example:

{
  "name": "bulk-index",
  "operation": {
    "operation-type": "bulk",
    "bulk-size": 5000,
    "looped": true
  },
  "time-period": 900,
  "clients": 10
}

Issues Resolved

[List any issues this PR will resolve]

Testing

• New functionality includes testing

[Describe how this change was tested]

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[gkamat]

It might be useful for "looped" to be an integer instead, which would indicate the number of iterations to loop. That would operate as in iteration-based mode and the user could specify "1000" for a thousand iterations, and "0" for infinite -- the current behaviour.

[opensearch-trigger-bot]

The backport to 1.16 failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/backport-1.16 1.16
# Navigate to the new working tree
pushd ../.worktrees/backport-1.16
# Create a new branch
git switch --create backport/backport-968-to-1.16
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 0522e68f577d2e99de76a516321932eef53313e5
# Push it to GitHub
git push --set-upstream origin backport/backport-968-to-1.16
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-1.16

Then, create a pull request where the base branch is 1.16 and the compare/head branch is backport/backport-968-to-1.16.