Alter BuildTargets and Setup function signatures to accept a struct with more info

[elliesterner]

Initially I wanted to simply send the VaultBenchmarkCoreConfig struct in this BuildTargets function. But the config package imports the benchmarktests package, so I couldn't import config into benchmarktests because it would be a circular dependency. Instaed, I created a new struct that lives in benchmarktests that represents the "top level" configuration (nothing test specific) called TopLevelTargetConfig.

This allows us to do more with our setup function. For example, check if the max_exp_jwt of the GCP role is less than the duration of the tests, an error will be returned immediately. (This GCP specific logic will be added in this follow up [PR])(#139).

2023-07-20T08:30:38.282-0500 [INFO]  vault-benchmark: setting up targets
2023-07-20T08:30:38.286-0500 [ERROR] vault-benchmark: target setup failed: GCP role max_jwt_exp (2s) cannot be shorter than benchmark test duration(20m0s)

[davidadeleon]

Good start! I do think there are some changes we may want to consider which I commented on.

[jasonodonnell]

One question but looks good to me!

[davidadeleon]

Looks good!