Minor: Incomplete validation of the GenesisState of the LightClient module

[danwt]

In x/lightclient/types/genesis.go:11-22 the Validate function of the GenesisState of the LightClient module is incomplete.
Specifically, the CanonicalClients slice is not deduplicated, allowing duplicate entries to be stored.
Additionally, the HeaderSigners slice is not validated to containing non-empty strings and does not include a mechanism to prevent duplicates as well.
These shortcomings could result in inconsistent states and inefficient storage usage.
Recommendation
We recommend enhancing the Validate function by implementing deduplication for the CanonicalClients slice and introducing string validation for the HeaderSigners slice to disallow empty entries.

[NagaTulasi]

Hi @mtsitrin, I would like to work on this.