feat(import): support engine path

[FalcoSuessgott]

fixes #276 based on #277.

• detect the engine path from the input if possible
• support -e in vkv import
• correctly append -p when using -e.
• docs
• test suite (see below)

test cases

• secrets imported, exported from original path
• secrets imported with overwritten path, exported from overwritten path
• import secrets, overwrite path with engine path, export from engine path
• import secrets, overwrite path with engine path and subpath, export from engine path
• import secrets, overwrite path and subpath, read from path

[codecov]

Codecov Report

Attention: Patch coverage is 69.65517% with 44 lines in your changes missing coverage. Please review.

Project coverage is 71.55%. Comparing base (6b528bc) to head (f391783).
Report is 104 commits behind head on master.

Files	Patch %	Lines
cmd/import.go	70.51%	13 Missing and 10 partials ⚠️
pkg/vault/engine.go	60.00%	5 Missing and 5 partials ⚠️
pkg/printer/secret/secret_printer.go	37.50%	5 Missing ⚠️
pkg/printer/secret/base.go	25.00%	3 Missing ⚠️
cmd/export.go	77.77%	1 Missing and 1 partial ⚠️
pkg/utils/utils.go	94.73%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #280      +/-   ##
==========================================
+ Coverage   69.59%   71.55%   +1.96%     
==========================================
  Files          29       35       +6     
  Lines        1322     1596     +274     
==========================================
+ Hits          920     1142     +222     
- Misses        290      315      +25     
- Partials      112      139      +27     

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