feat: add vault-path validation

[c0deltin]

Description

Users should have the ability to additionally validate vault paths. For example to prevent path traversals.
This can be enabled by setting a regular expression to the new environment variable AVP_PATH_VALIDATION.

This pull requests relates to the issue #418.

Checklist

Please make sure that your PR fulfills the following requirements:

• Reviewed the guidelines for contributing to this repository
• The commit message follows the Conventional Commits Guidelines.
• Tests for the changes have been updated
• Are you adding dependencies? If so, please run go mod tidy -compat=1.17 to ensure only the minimum is pulled in.
• Docs have been added / updated
• Optional. My organization is added to USERS.md.

Type of Change

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• New tests
• Build/CI related changes
• Documentation content changes
• Other (please describe)

Other information

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Merging #454 (6c144b3) into main (ec1bd7a) will increase coverage by 0.19%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #454      +/-   ##
==========================================
+ Coverage   77.17%   77.36%   +0.19%     
==========================================
  Files          23       23              
  Lines        1485     1498      +13     
==========================================
+ Hits         1146     1159      +13     
  Misses        252      252              
  Partials       87       87              

Impacted Files	Coverage Δ
cmd/generate.go	71.08% <100.00%> (+1.85%)	⬆️
pkg/kube/template.go	88.00% <100.00%> (+1.04%)	⬆️
pkg/kube/util.go	90.25% <100.00%> (+0.20%)	⬆️

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