feat: Add support for URL custom property value type

[IrvingMg]

Since ValueType is just a string field with no validation, I only updated the documentation comment and added a test. Let me know if I'm missing something.

Fixes#3878

[stevehipwell]

It might make sense to add type for ValueType?

[IrvingMg]

It might make sense to add type for ValueType?

I think it would make sense. However, as I see it, the pattern in the library is to use similar enum-like fields as plain strings with documentation comments, such as:

go-github/github/repos.go

Lines 75 to 78 in 07ddcd9

	SquashMergeCommitTitle*string`json:"squash_merge_commit_title,omitempty"`// Can be one of: "PR_TITLE", "COMMIT_OR_PR_TITLE"
	SquashMergeCommitMessage*string`json:"squash_merge_commit_message,omitempty"`// Can be one of: "PR_BODY", "COMMIT_MESSAGES", "BLANK"
	MergeCommitTitle*string`json:"merge_commit_title,omitempty"`// Can be one of: "PR_TITLE", "MERGE_MESSAGE"
	MergeCommitMessage*string`json:"merge_commit_message,omitempty"`// Can be one of: "PR_BODY", "PR_TITLE", "BLANK"

But if you’re okay with adding types, I could add constants like:

const (
PropertyValueTypeString="string"PropertyValueTypeSingleSelect="single_select"PropertyValueTypeMultiSelect="multi_select"PropertyValueTypeTrueFalse="true_false"PropertyValueTypeURL="url"
)

And we can decide later if we want to add similar enums for other fields across the library.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.48%. Comparing base (07ddcd9) to head (1356164).
⚠️ Report is 13 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@## master #3879 +/- ##
=======================================
Coverage 92.48% 92.48% =======================================
Files 200 200 Lines 14564 14564 =======================================
Hits 13469 13469 Misses 895 895 Partials 200 200 

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[stevehipwell]

@IrvingMg this pattern is used elsewhere here.

[IrvingMg]

@IrvingMg this pattern is used elsewhere here.

I’ve added the constants. I considered using a type alias, but I believe that would be a breaking change, and I wasn’t sure we wanted to introduce one.

[gmlewis]

LGTM.
Awaiting second LGTM+Approval from any other contributor before merging.

cc: @stevehipwell - @alexandear - @zyfy29

[gmlewis]

Thank you, @alexandear!
Merging.