Feat: Add setItemIfNotExists option to set storage value if not exists

[lukashenkor]

This pull request adds setItemIfNotExists option to set storage value if not exists in useLocalStorage and useSessionStorage.

Sometimes it could be necessary to have initialized storage value if it not exists. It is much easier and cleaner to provide just one simple boolean option.

Please let me know if there's something that I missed.

[changeset-bot]

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Latest commit: b7fdbbb

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