Track node index status and support proxy header to require indexed nodes

[tombeynon]

• Track whether nodes have indexing enabled and expose this info via the status.cosmos.directory endpoints
• Allow a header when using the REST and RPC proxies to limit request to indexed nodes. Potentially x-cosmos-index-enabled ?

See conversation on Chain Registry https://github.com/cosmos/chain-registry/issues/1005

[tombeynon]

Note x-cosmos-block-height header mentioned here: https://github.com/cosmos/cosmos-sdk/issues/9465

[koen84]

What's the status here ? Very annoying to error from all the nodes missing indexed data.