Hotfix/pending hotkey emission on swap

[camfairchild]

Description

This hotfixes an issue with the hotkeyswap and the newPendingdHotkeyEmission maps.

Currently any hotkeys that swap will lose the pending hotkey emission, being recorded as an entry in the Stake map Stake(old_hotkey, 0x0000) (default AccountId).

This PR fixes the swap functions for coldkey and hotkey and adds a migration for two known hotkey swaps.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run cargo fmt and cargo clippy to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules