Change argument `env.samples` in `get.emsemble.samples()` to optional

[ecamo19]

Changes argument env.samples in the get.ensembles.samples() function from required to optional

env.samples is a required argument in the get.ensemble.samples function. However not all the time these env samples are available. Thus, is necessary to change this argument to optional in case a user wants to get the ensemble samples without taking into account the env.samples.

Description

The argument changes from required to optional, if the argument env.samples is NOT null the env.samples object will be appended to the pft.samples object.

Motivation and Context

With the change proposed it will be possible to get ensemble samples without having the env.samples object

Review Time Estimate

• [ ] Immediately
• [ ] Within one week
• [x] When possible

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] My name is in the list of CITATION.cff
• [ ] I have updated the CHANGELOG.md.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

[Aariq]

Was your issue fixed by https://github.com/PecanProject/pecan/pull/3005 ? If so, does this PR still need review?

[Aariq]

I converted this to a draft. I may pick this up and implement some of my suggestions later.