Add the ability to create reflists

[adam-wolfe]

Is your feature request related to a problem? Please describe.

Reflists enable users in ISPF to save a list of data sets for quick access. Zowe Explorer allows users to save search queries as favorites. However, the queries may include too many data sets or might exclude data sets that they also need access to. By allowing a user to build reflists, the user can more easily select exactly the data sets that they need to work with.

Describe the solution you'd like

Allow users to:

1. Create a reflist
2. Add data sets to the reflist
3. Open/expand the reflist

Question: Should it be possible for users to add data sets to a reflist from multiple LPARs?

Describe alternatives you've considered

Zowe Explorer allows users to save search queries as favorites. In many cases, this might be adequate.
 
Additional context

Related to #3013

[github-actions]

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