feat: add parity signer companion for polkadot vault support

[nud3l]

Interbtc UI Pull Request Template

Description

• Signing raw data as we require for the T&Cs is not supported in the polkadot.js extension version released in the Firefox and Chrome stores: Raw signing with polkadot.js and parity signer is not possible due to outdated polkadot.js extension version in Chrome and Firefox stores polkadot-js/extension#1268
• Users that use the Polkadot Vault hardware wallet (https://signer.parity.io/) cannot sign the T&Cs and thus not use our app. Once they signed the T&Cs, these users can use polkadot.js in combination with the Polkadot Vault to sign transactions
• This PR adds https://github.com/paritytech/parity-signer-companion as a wallet option that allows signing raw data
• Users can use the parity signer companion extension to sign T&Cs and then choose to continue using the parity signer companion or the polkadot.js extension

Current behaviour (updates)

The possible wallets to select are polkadot.js, talisman, and subwallet.

New behaviour

Add the parity signer companion.

Reproducible testing steps:

1. Open the select wallet modal and see Parity Signer Companion as an option
2. Install Parity Signer Companion and add a wallet. See that you can sign the T&Cs

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