cli: Expose --account flag for solana-test-validator in Anchor.toml

[tomlinton]

Add test.validator.account to the toml with filename/address to expose --account. I also moved test.clone to test.validator.clone for consistency. I think all the validator configuration flags should live under test.validator.

Example:

[provider]
cluster = "localnet"
wallet = "~/.config/solana/id.json"

[programs.localnet]
basic_0 = "Fg6PaFpoGXkYsidMpWTK6W2BeZ7FEfcYkg476zPFsLnS"

[scripts]
test = "yarn run mocha -t 1000000 tests/"

[test.validator]
url = "https://api.mainnet-beta.solana.com"

[[test.validator.clone]]
address = "9s3RbNan8nLetHoGFVgCJ4fABF3f5ha9dxcGqSdFrD9e"

[[test.validator.account]]
address = "Ev8WSPQsGb4wfjybqff5eZNcS3n6HaMsBkMk9suAiuM"
filename = "test_account.json"

[[test.validator.account]]
address = "H4YJ7ESVkiiP9tGeQJy9jKVSHk98tSAUD3LqTowH9tEY"
filename = "test_account.json"

Closes #1260