parameterize block explorer URLs and move to hardhat config

[mattstam]

Description

Merges the two different functions we have into one, and move into hardhat config, which seems better suited for this since it:

1. is near the rest of the network configs
2. is a better place to be references globally by the project

Suggested by @DmitriyShepelev here.

Test Coverage

N/A

• My commit message contains my Ethereum address.
• My code follows the Style Guide.
• My code requires a Documentation Update.