Add ART and ATP to 'support top api' command

[aweisser]

Community Contribution License

All community contributions in this pull request are licensed to the project maintainers
under the terms of the [Apache 2 license] (https://www.apache.org/licenses/LICENSE-2.0).
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contributions to the project maintainers under the Apache 2 license.

Description

The "mc support top api" command already displays the RX, TX, CALLS, and ERRORS.
This commit adds the average request time (ART) and the average throughput (ATP) to the output.

Average Request Time (ART) = Total Duration / Calls
Average Throughput (ATP) = (RX+TX) / Total Duration

Motivation and Context

There already was a TODO comment about ART in the code.
With ATP and ARP added to the output the user can get a quick impression on the current "performance" of his API calls.

How to test this PR?

Execute mc support top api TARGET and watch the output.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Optimization (provides speedup with no functional changes)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Fixes a regression (If yes, please add commit-id or PR # here)
• Unit tests added/updated
• Internal documentation updated
• Create a documentation update request here