Minor: add standard deviation measurement to the end to end latency test

[cliu0013]

More detailed description of your change,
if necessary. The PR title and PR message become
the squashed commit message, so use a separate
comment to ping reviewers.

We have been trying to benchmark a DDS application by comparing it to Kafka. Added standard deviation measurement in the end to end latency test.

Summary of testing strategy (including rationale)
for the feature or bug fix. Unit and/or integration
tests are expected for any behaviour change and
system tests should be considered for larger changes.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)