Replace PLP hard coded border-radius with variable

[kirsty-hames]

Subject of the enhancement

PLP indicator border-radius is hardcoded at 50px in the plugin LESS.

    border-radius: 50px;

The only border values editable in Vanilla currently are border colours via variables e.g. @progress-border.

PLP indicator as standard looks like this:

Expected behaviour

border-radius to be available in Vanilla via variable such as @progress-border-radius. Default value should be set at 50px for consistency with the plugin value.

[github-actions]

🎉 This issue has been resolved in version 9.16.0 🎉

The release is available on GitHub release

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