[pkg/stanza] Fix Stanza Key Value Parser custom pair delimiter bug

[dpaasman00]

Description:
Fixes a bug that would occur where quotes were not respected while pair parsing with a custom pair delimiter. This occurred because in the case of a custom pair delimiter strings.Split() was used which does not respect quotes. This bug was only an issue with custom pair delimiters because the default white space delimiter used strings.FieldsFuncwith a function that did respect quotes.

This fix adds the function splitPairs(input, pairDelimiter string) ([]string, error) which will split the given input on the given pairDelimiter.

Alternative solutions like strings.FieldsFunc and csv.NewReader were considered but not used because they require the delimiter be a rune. This would have worked in many cases except for when the delimiter is more than 1 unique character long. Since the delimiter shouldn't be limited to a single rune, those solutions were rejected.

A consequence of this new function respecting quotes is it will fail and return an error if any quoted value is ever malformed. For example, given the input k1=v1 k2='v2" the function will return an error because the single quote used for k2's value is never closed. It will also fail on the input k1='v1 k2=v2 k3=v3 for the same reason that the quote is never closed. I believe this is the behavior we want so that we don't return incorrect pairs for further parsing.

Link to tracking Issue:
Closes #31034

Testing:
Added in additional unit tests to verify correct behaviors.

Documentation:
I don't believe documentation is required as the user shouldn't see any changes to intended behavior.