initial update to load plugins from file

[nirrozenbaum]

This PR adds plugins configuration loading from file and is starting to handle some cleanup.
There are still follow up PRs that are needed to complete cleanup, but main path in cmd/runner and in e2e tests is complete.
additional minor changes were done to update some of the plugin names for readability purpose. for example random picker plugin name was called random, update to random-picker since it's not possible to understand what does plugin random means (same update was done to almost all plugins).

out of this PR and handled in follow up PRs to keep each PR scoped and relatively small and focused:

• conformance test: should move the predictable filter (and its test) that is used in conformance tests to the same place as other plugins and register it in the plugins registry. after that is done, we should be able to load conformance config from file using configmap the exact same way that is done in this PR - done in load plugins from file in conformance tests #1152.
• removal of NewScheduler function from scheduler.go. this includes updates in several places like integration tests and scheduler unit-test and may be a big PR on its own. therefore left this point to a separate PR which will be tightly scoped for this purpose - done in remove NewScheduler function #1153.
• removal of initializeScheduler function from runner: after the two first points are handled, we can safely remove this function - done in remove NewScheduler function #1153.

after the above is done, we should make sure any additional env var loading, helper functions or variables that were used to initialize plugins config are all removed. none of those should exist in code anymore.

cc: @ahg-g @kfswain @elevran @shmuelk

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[ahg-g]

Great to see the runner.go file getting lighter!

How did we test that the config file is generating the same hard coded configuration?

[nirrozenbaum]

Great to see the runner.go file getting lighter!

How did we test that the config file is generating the same hard coded configuration?

@ahg-g I tested it manually, both options default + v2, and added some logging to this PR to validate that.

[ahg-g]

Probably useful to use some prefix indicating that this will be removed, perhaps experimental-with-prefix-cache-scorer.yaml?

[nirrozenbaum]

scheduler-v2 will not be removed, the default will be removed.
v2 will become the new default.

[ahg-g]

/lgtm