Implement versioning between VPR and stack docs

[karenzone]

Follow-up to #46

• Karen: Test implementation on a single plugin: [input-file] Doc: Set version attribute in plugin source file #308
• Karen: Evaluate exposing version information relevant to this comment: Solve versioning between VPR and stack docs #46 (comment)
• Karen: Implement on relevant plugins (mini-meta issue to come)

Phase 1: Implement for plugins most likely to cause versioning errors (source and older versions)

• input-beats
• input-elasticsearch (?)
• input-file
• input-
• filter-elasticsearch
• output-elasticsearch

Phase 2: Implement for ECS-compatible plugins (source and older versions)

• input-

Notes to self @karenzone:

• Test version implementation for input-file