Add section about delay server migration

[korydraughn]

• main
• 4-3-stable

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As of right now, there's no documentation which covers delay server migration.

Please add a section which covers the following:

• R_GRID_CONFIGURATION options
• delay server leader and successor
• delay queue
• delay rule locking (iRODS 5 only)

[alanking]

I would like to request expanding this to be a comprehensive page about the delay server which would include things like explanation of its use and how it is configured. The process model explains sort of where it sits in relation to the server, but I think more context would be helpful to write down.