[BEAM-9500] [WIP] Refactor load tests

[pjotrekk]

Changed the input to be initialized in the base class instead of the subclasses.

Minor:

• Replaced creating new TimeMonitors with the one from the superclass
• Added type to List at LoadTest:104
• Moved initializing ByteMonitor object to constructor instead of creating it ad hoc

related: #10949

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---		---	---
Java
Python		---			---	---
XLang	---	---	---		---	---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website
Non-portable
Portable	---		---	---

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[pjotrekk]

@mwalenia

[pjotrekk]

I think there is a lot more to do with the part "make LoadTest parameterized instead of a base class."

[stale]

This pull request has been marked as stale due to 60 days of inactivity. It will be closed in 1 week if no further activity occurs. If you think that’s incorrect or this pull request requires a review, please simply write any comment. If closed, you can revive the PR at any time and @mention a reviewer or discuss it on the dev@beam.apache.org list. Thank you for your contributions.

[aaltay]

@piotr-szuberski - what is the next step for this PR? Is it still active? Should we close it?

[stale]

This pull request has been marked as stale due to 60 days of inactivity. It will be closed in 1 week if no further activity occurs. If you think that’s incorrect or this pull request requires a review, please simply write any comment. If closed, you can revive the PR at any time and @mention a reviewer or discuss it on the dev@beam.apache.org list. Thank you for your contributions.

[pjotrekk]

@piotr-szuberski - what is the next step for this PR? Is it still active? Should we close it?

Sorry for such delay, I totally forgot to response. I'll close this PR as it's not that important and far outdated.