Add new fields to ChainIdentity and SubnetIdentity structs

[basfroman]

Context

1. ChainIdentity struct has the following fields:

• name
• url
• image
• discord
• description
• additional

It would be useful to have link to the github repository as additional field github_repo in ChainIdentity struct

2. SubnetIdentity struct has the following fields:

• subnet_name
• github_repo
• subnet_contact

It would be useful to have link to the websire/any other link as additional field url in SubnetIdentity

AC:

• ChainIdentity has github field
• SubnetIdentity has url field