Provide more information to users in regards to pricing

[cmwaters]

Feature Request

When blocks are full, inclusion is decided based on a first price auction of the gas price of the transactions. Currently it's difficult to get information to make decisions on what bid a users should make. To make such information more accessible I propose:

• Transactions that don't make it into the mempool because of an insufficient price should state what the minimum price is to get into the mempool and an estimation of the minimum price to get into the next block.
• [Optionally] A MempoolInfo endpoint should be exposed that also contains that information: Minimum gas price for mempool and block

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