Support from clause for resources in Conditionals

[dibyom]

Expected Behavior

Resources in Conditions should be able to use output resources from other tasks using the from clause. This will become very important when we have resource immutability and new output resources are created from the original resource spec.

On generating the pod for conditions, if 'from' is used for the condition's resource, the pod could mount to that resource (e.g. /pvc/) then copy to condition resource's workspace.
This is similar to Task usage in the pipeline.

Actual Behavior

No support 'from', any Git resource declared for the condition will be handled as normal Git fetch.

Steps to Reproduce the Problem

1. Define a normal Condition check with resource type Git
2. Use that Condition in the pipeline, expect 'from' can be used

Additional Info

Originally posted by @bobcatfish in #1151:

Hmm something just occurred to me - can conditions use the from clause for resources? If there is more work to do here I totally would expect that in a follow up PR, but basically what I'm thinking is that if a Task is getting a resource from another Task, but has some condition to execute on that resource, the user would probably want the condition to be executed on that same task
e.g. a Task has a git output (assuming a world where a git output creates a new commit), another Task gets the git resource from that task, but the condition says only if the most recent commit changed XYZ files (kind of contrived but maybe??)

Issue updated with #1499