[Core Feature] FlyteAdmin/Propeller should allow offloaded workflow specs

[kumare3]

Motivation: Why do you think this is important?
There are cases in which the spec increases to a very large size - workflowtemplate or tasktempaltes with queries are very large. Also having the spec in etcD does not really offer any benefit.

Goal: What should the final outcome look like, ideally?
When a user executes a workflow, instead of writing the entire workflow to the CRD, we could write the spec to the Blob store and just pass a reference. This would have following benefits

1. Extremely large workflow graphs (today Flyte supports workflow graphs in order of 5k, but this is subject to size of a task). This could increase graph to be arbitrarily large.
2. Faster sync loops with etcD. This will improve transition performance

Describe alternatives you've considered
Spec compression. This is very complicated and debugging will be harder.

[Optional] Propose: Link/Inline OR Additional context
Instead of the inline spec - we can just have a reference to the spec in blob store - https://github.com/flyteorg/flytepropeller/blob/master/pkg/apis/flyteworkflow/v1alpha1/workflow.go#L29

[hamersaw]

Completed in #2705