Add docs around Validator Management Protocols

[meaghanfitzgerald]

Request

Add high-level, explanatory document explaining the main usage differences between the PoA Validator Manager, Erc20StakingManager, and NativeTokenStakingManager to the the EVM Customization page.

Solution

1. In the Avalanche Protocol section, add a doc:

• explaining how Avalanche L1s can enforce any validation logic that can be encoded via smart contract
• explaining when and why an organization would want to run a PoA chain or a PoS chain

2. In the Validator Manager section, add a doc:

• explaining basic concepts of PoA and PoS networks
• explaining how validators are added and removed from L1s using the PoA Validator Manager
• explaining how validators are managed by the Erc20StakingManager and NativeTokenStakingManager, noting the difference between staking tokens
• explain how validators in Erc20 or PoS L1s are rewarded for validation

References

• https://academy.avax.network/guide/etna-upgrade-motivation
• https://academy.avax.network/guide/etna-changes#for-existing-l1s