feat!(VoiceConnection): add disconnect and rename reconnect to rejoin

[amishshah]

Please describe the changes this PR makes and why it should be merged:

• Adds VoiceConnection#disconnect if you want to keep the VoiceConnection instance while still disconnecting from voice.
• Rename VoiceConnection#reconnect to VoiceConnection#rejoin for accuracy (it actually attempts to rejoin the voice channel, not just the voice server)
• Rename VoiceConnection#reconnectAttempts to VoiceConnection#rejoinAttempts
• Allow VoiceConnection#rejoin to take a partial JoinConfig. For example, vc.rejoin({ channelId: 'newid' })

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• This PR changes the library's interface (methods or parameters added)
• This PR includes breaking changes (methods removed or renamed, parameters moved or removed)

[codecov[bot]]

Codecov Report

Merging #129 (8b08aa4) into main (e9c3a94) will increase coverage by 0.97%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #129      +/-   ##
==========================================
+ Coverage   66.25%   67.22%   +0.97%     
==========================================
  Files          19       19              
  Lines         880      891      +11     
  Branches      214      218       +4     
==========================================
+ Hits          583      599      +16     
+ Misses        295      290       -5     
  Partials        2        2              

Impacted Files	Coverage Δ
src/VoiceConnection.ts	85.49% <100.00%> (+5.49%)	:arrow_up:

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