Allow slashes in the flag name regex

[wildefires]

Upstream issue: #315

Description

Allows you to add a as a valid character in a flag name to allow for sensible namespacing

Motivation and Context

Allows people to namespace in a unix type fashion that makes it clear where the namespace ends and the flag begins

How Has This Been Tested?

Tested locally against existing postgres database; was able to update a flag and then get the flag back successfully

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-io]

Codecov Report

Merging #316 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #316   +/-   ##
=======================================
  Coverage   81.88%   81.88%           
=======================================
  Files          26       26           
  Lines        1535     1535           
=======================================
  Hits         1257     1257           
  Misses        209      209           
  Partials       69       69

Impacted Files	Coverage Δ
pkg/util/util.go	100% <ø> (ø)	⬆️

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