Narrative Overhaul: Rename ENSv2 Plugin to Omnigraph

[shrugs]

• pending confirmation on 'omnigraph' naming
• rename the ensv2 plugin to omnigraph
• update all usage across the project
• ensure that the ENSv2Root datasource remains as-is
• any usage of graphql-api should be omnigraph (prerequisites, some libs)
• endpoint to /api/omnigraph
• ENSNODE_GRAPHQL_API_URL becomes ENSNODE_OMNIGRAPH_API_URL
• apps/ensapi/src/handlers/api/graphql/ensnode-graphql-api.ts becomes apps/ensapi/src/handlers/api/omnigraph/omnigraph-api.ts (maybe omnigraph.handlers.ts)
• also applies to ensadmin's api/graphql becoming /api/omnigraph
• etc etc

[coderabbitai]

🔗 Related PRs

#1566 - feat: separate ensv2 datasources out more correctly [merged]
#1575 - fix: add correct ensv1 and ensv2 addresses to sepolia-v2 namespace [merged]
#1670 - ENSv2 Integration Updates [merged]
#1730 - Remove Core Plugin Restriction [merged]
#1758 - fix: allow ensv2 apis to be used without ensv2 datasource [merged]

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