Significant retention.sh Update

[metanull-operator]

Major retention.sh update to generalize functionality, add configurability, improve error checking, add more client support, etc.

• Retained ability to set default value of variables in the script, but now also supports environment variables and loading an environment variable file
• Added timeout_window variable to configure timeout for resetting clients
• Client systemd service names must now be defined to support different system setups
• Client type must be defined for each client to support different logic for various clients
• Ownership and group of testnet files can now be reset after downloaded latest files, in case specific ownership is required
• FORCE_RESET option added to force a reset of the clients for testing purposes
• Additional error checking around parameters
• External command calls updated to avoid injections into commands
• Execution data directory logic now retains enode info for reth, geth, besu, nethermind and erigon
• Logic updated to support single-client consensus/validator clients or separate consensus and validator clients
• Slashing database cleared for lodestar, prysm, lighthouse, teku, and nimbus validator clients in both single-process and separate-process configurations
• Genesis initialization added for erigon
• Optionally run geth and erigon initialization as a non-root user, for instances where the service doesn't run as root
• Additional error handling around retrieval of GitHub release information