Adds banner notifying of testnet deprecation.

[plor]

• displays on testnet DAOs

GitHub Issue

fixes #1956

Changes

Show a banner (open to wording changes) notifying users of Rinkeby EOL. Should this show for all users or only for testnet DAOs (currently shows only for Rinkeby or Goerli DAOs).

Packages Added

N/A

Checks

Before making your PR, please check the following:

• [x] Critical lint errors are resolved
• [x] App runs and builds locally