Document how to identify installed Elyra version

[ptitzler]

Adds a new section to the troubleshooting documentation topic that outlines how users can determine which Elyra version is installed.

• The listed approaches are ordered by simplicity.
• The first three approaches are only supported by newer Elyra versions. The last (most generic) approach should work for all versions.

What changes were proposed in this pull request?

See above

How was this pull request tested?

Reviewed the output of make docs

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[elyra-bot]

Thanks for making a pull request to Elyra!

To try out this branch on binder, follow this link:

[kevin-bates]

Looks good. Thanks @ptitzler