`Rep Nomination` document type processing.

[Mr-Leshiy]

Summary

Implement a Rep Nomination specific validation according to the specification.

Details

• Add a new RepNominationRule with the corresponding CatalystSignedDocumentValidationRule trait implementation.
• Add a constructor

    pub async fn new<Provider>(
        doc: &CatalystSignedDocument,
        provider: &Provider,
    ) -> anyhow::Result<Self>
    where
        Provider: CatalystSignedDocumentProvider,
    {
        if doc.report().is_problematic() {
            anyhow::bail!("Provided document is not valid {:?}", doc.report())
        }
        anyhow::ensure!(
            doc.doc_type()? == &REP_NOMINATION,
            "Document must be Contest Ballot type"
        );
     // perform the same set of validation as for the `CatalystSignedDocumentValidationRule`
    ...
}

• Add a corresponding test cases