CirrusMain checkpoint 2_827_550

[quantumagi]

See https://app.clickup.com/t/1dyq4z2.

It appears that the CirrusMain chain contains a few blocks that were mined by older/minority versions of the node that would not be mineable with the latest code version. The situation probably came about due to many of the newer nodes not being able to mine at the time.

The purpose of this PR is to exclude the blocks which led to "block timestamp too early" errors from the PoAHeaderSignatureRule rule by virtue of this existing code:

        public override async Task RunAsync(RuleContext context)
        {
            // Only start validating at the last checkpoint block.
            if (context.ValidationContext.ChainedHeaderToValidate.Height < (this.lastCheckPoint?.Height ?? 0))
                return;

            ChainedHeader chainedHeader = context.ValidationContext.ChainedHeaderToValidate;