Update Go Version to 1.20 for IBC-Apps Compatibility

[papadritta]

This PR updates the Go version requirement from 1.19 to 1.20 for the Xion project. The update is necessary to resolve a build error encountered when compiling the packet-forward-middleware module, which requires Go 1.20 due to its reliance on the errors.Join function introduced in this version.

Error Encountered:

# github.com/cosmos/ibc-apps/middleware/packet-forward-middleware/v7/packetforward/keeper
../go/pkg/mod/github.com/burnt-labs/ibc-apps/middleware/packet-forward-middleware/v7@v7.1.3-0.20240308232808-736bd51c54ad/packetforward/keeper/keeper.go:172:73: undefined: errors.Join
note: module requires Go 1.20
make: *** [Makefile:94: install] Error 2

Changes Made:

• Updated documentation in docs/build-the-xion-daemon.md to reflect the new Go version requirement.
• Updated all relevant configuration files and scripts to use Go 1.20.

This change ensures compatibility with batch-forwarding software and any future dependencies requiring newer Go features.

[justinbarry]

Good catch @papadritta. We can update all the way to 1.21! I'll update it. Much appreciated!