Split AR Encryption config settings into sections [ci-skip]
Split AR Encryption config settings into sections [ci-skip]

This splits the table of `config.active_record.encryption.*` settings
into individual linkable sections, similar to the Configuration guide.

This also bumps up the advice about using credentials, adds a few
backticks in the appropriate spots, and fixes a link which always
pointed to the latest version of the Configuration guide.

yawboakye/rails,BlakeWilliams/rails,kmcphillips/rails,yawboakye/rails,Erol/rails,yahonda/rails,georgeclaghorn/rails,rails/rails,BlakeWilliams/rails,Erol/rails,georgeclaghorn/rails,esparta/rails,kmcphillips/rails,esparta/rails,BlakeWilliams/rails,MSP-Greg/rails,Edouard-chin/rails,yahonda/rails,BlakeWilliams/rails,yahonda/rails,yawboakye/rails,rails/rails,yawboakye/rails,Edouard-chin/rails,kmcphillips/rails,esparta/rails,MSP-Greg/rails,kmcphillips/rails,Edouard-chin/rails,Erol/rails,rails/rails,MSP-Greg/rails,MSP-Greg/rails,Erol/rails,yahonda/rails,georgeclaghorn/rails,esparta/rails,georgeclaghorn/rails,rails/rails,Edouard-chin/rails