Integrate account_token and link_token into the Gem

[cdrrazan]

Notes

• The initially implemented integrationclient doesn't follow the regular pattern used in this gemfile. Therefore, it is been refactored and moved to provider.
• Account_token retrieval and link_token creation flow have been integrated into the gem.

Sample Usage

1. Create link_token

client_integration_link_token = client.integrations.link_token.create(
      end_user_origin_id: user.recognize_hashid,
      end_user_organization_name: user.company.name,
      end_user_email_address: user.email,
      categories: ,
      integration: provider
    )
client_integration_link_token.link_token

2. Retrieve account_token based on public token

account_token_result = client.integrations.account_token.retrieve(public_token: )
account_token_result.account_token