Move loadGenerationDelay to Benchmark

Currently, Executions define a loadGenerationDelay:

apiVersion: theodolite.com/v1
kind: execution
spec:
  execution:
    loadGenerationDelay: 30 # in seconds

With our restructurings in #270 (closed) and #272 (closed), it would be more appropriate to move this delay to the Benchmark:

apiVersion: theodolite.com/v1
kind: benchmark
spec:
  loadGenerator:
    delaySeconds: 30

Note the slightly changed name. It might also be reasonable to add fields, such as delayBeforeSeconds and delayAfterSeconds as well as to add these fields also to sut and infrastructure, but I don't have a use case for this so far.

added Nice To Have modul/theodolite labels

changed title from Move load generation delay to Benchmark. to Move loadGenerationDelay to Benchmark

changed the description