Dogecoin Optimization Flags

These should not be strictly required with the fixes in thorchain/thornode!3416 (merged), but there are some small positive effects and we might as well after recent pain.

• The dbcache should provide some small improvement in disk utilization.
• The rpcthreads increase has no observed effect, but could perhaps be relevant for operators sharing between more Bifrosts.
• The minrelaytxfee will drastically decrease the node-local mempool count. Some small fee inbounds may be skipped until they are mined, but that should pose no problem. Separately all outbounds tend to have over an order of magnitude higher fee - but in any case, observing outbounds in the mempool should no longer matter, since the insta-observe now prevents cross-block reschedule. Additionally the change in thorchain/thornode!3416 (merged) defaults to DOGE mempool scanning disabled.
• The harddustlimit and mempoolreplacement flags are mostly irrelevant with the high minrelaytxfee, but may filter a bit more mempool spam to further reduce any load.
• Memory request was increase after observation of higher utilization with the new cache setting.