standard way to refer to DVC-files and other terms

[jorgeorpinel]

There 's several ways in which the docs refer to DVC-files (meaning the stage files created by dvc add, dvc run, etc, with the .dvc file extension).

Standardize everything to "DVC-file(s)" throughout the docs EXCEPT if the phrase is used for OTHER DVC-related files (not stage files) i.e. in "DVC Files and Directories":

• "DVC file" and plural "DVC files". <-- Do NOT use for stage files

• "DVC-file" and its plural "DVC-files". <-- Use this one

• ".dvc file(s)" or ".dvc file extension" <-- Avoid except in single doc where DVC-files are described

• "stage file(s)" <-- Avoid except when in the context of data pipelines

  ^ Partially extracted this case to there's ambiguity between the terms "stage" and "stage file" #423

• DVC "metafile(s)"/"meta file(s)" <-- Avoid except in single doc where DVC-files are described

UPDATE: Other interesting phrases to review are: See #432

[jorgeorpinel]

Sorry, 2 of the checkboxes in the original description weren't completed with the PR that closed this. Reopened this issue and opened PR #433