Rename xdai ChainType config to gnosis

[friedemannf]

Reflect the current name of Gnosis chain by changing the ChainType config value from xdai to gnosis.

The old value of xdai is being deprecated but will continue to receive support for the next two upcoming releases (2.10 & 2.11). If it is being used, a value warning will be issued, reminding the user to switch to the new value. The bundled defaults for Gnosis mainnet & testnet already include the switch to gnosis, requiring no action by the user if no custom config has been set.

In 2.12, the old value of xdai will be removed, requiring all users to be updated to the new value by then.

[github-actions[bot]]

I see that you haven't updated any README files. Would it make sense to do so?

[cl-sonarqube-production[bot]]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube