[xcm-emulator] Chains generic over Network & Integration tests restructure (#2092)

Closes:
- #1383 
- Declared chains can be now be imported and reused in a different
crate.
- Chain declaration are now generic over a generic type `N` (the
Network)
- #1389
- Solved #1383, chains and networks declarations can be restructure to
avoid having to compile all chains when running integrations tests where
are not needed.
- Chains are now declared on its own crate (removed from
`integration-tests-common`)
- Networks are now declared on its own crate (removed from
`integration-tests-common`)
    - Integration tests will import only the relevant Network crate
- `integration-tests-common` is renamed to
`emulated-integration-tests-common`

All this is necessary to be able to implement what is described here:
paritytech/roadmap#56 (comment)

---------

Co-authored-by: command-bot <>

Author: NachoPal

.gitignore

@@ -17,7 +17,6 @@
 **/._*
 **/.criterion/
 **/*.rs.bk
-**/chains/
 **/hfuzz_target/
 **/hfuzz_workspace/
 **/node_modules