adding custom cluster separable job name option

[ac-optimus]

fixes #224

Description

Motivation and Context

Types of Changes

• Documentation update
• Bug fix
• New feature
• Breaking change¹

¹The change breaks (or has the potential to break) existing functionality.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• My code follows the code style guideline of this project.
• The changes introduced by this pull request are covered by existing or newly introduced tests.

If necessary:

• I have updated the API documentation as part of the package doc-strings.
• I have created a separate pull request to update the framework documentation on signac-docs and linked it here.
• I have updated the changelog.

[b-butler]

LGTM

[b-butler]

@bdice approves.

[csadorf]

How would a user find out about this feature?

[bdice]

How would a user find out about this feature?

@csadorf I think that's a good question. I created an issue with a suggestion for documenting this. I'm open to alternative ideas as well: glotzerlab/signac-docs#81