Support specify more flexible gas price on feemarket chains

[yihuang]

Summary

Since the introduction of priority mempool and feemarkets, we need more flexibility to customize the tx building process, mainly the gas price-related stuff.
Also as a workaround of the tx reorder issue, we need different strategies for different chains to control the tx priority:

• With the SDK default mechanism plus this fix, the current static gas price works fine.
• With the feemarket introduced in ethermint, we need to add an extension option(ExtensionOptionDynamicFeeTx) to specify a max_priority_price.

Problem Definition

Proposal

• Change the type of config::GasPrice to sth like:

  enum GasPrice {
    Static(string, f64),
    EthermintDynamicFee(string, f64, u64),
  }

• Update tx building logic accordingly.

• Add a config item to specify extension options for the tx.

  enum ExtensionOption {
    EthermintDynamicFee(string),
  }

Acceptance Criteria

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate milestone (priority) applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned