feat: implemente Msgs for SP exit

[alexgao001]

Description

This PR adds required msg for SP exit.

A SP exit process is outlined below:

1. The SP which wants to exit to send a tx with MsgStorageProviderExit, it is status will become STATUS_GRACEFUL_EXITING.
2. All other SPs are encouraged to be the successors of the exiting SP's Global Virtual Group family(GVGF) as primary SP, or Global Virtual group(GVG) as secondary. They can send a tx with MsgReserveSwapIn to reserve the position.
3. Once successor got all data stored properly. They will send a tx with MsgCompleteSwapIn to ack the success, within GVGF/GVG, SP replacement will take place.
4. If the SP has no more GVGF/GVG related, it can send a tx with MsgCompleteStorageProviderExit to complete the exit, deposit onto Greenfield will be refund.

Rationale

Example

add an example CLI or API response...

Changes

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Potential Impacts

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