allow rollup client update with multiple DA header update

[rnbguy]

Currently, the sovereign header has a single update header from DA.

sovereign-ibc/clients/sov-celestia/types/src/client_message/header.rs

Lines 21 to 24 in f0d38de

	pub struct Header<H> {
	pub aggregated_proof: AggregatedProof,
	pub da_header: H,
	}

But it may happen, the DA header needs multiple updates to reach to the latest height. Currently, this requires creating multiple sovereign headers - which needs redundant queries to rollup endpoint for the rollup state roots.

This can be avoided by passing the required (possibly, multiple) DA headers in a single sovereign header.

pub struct Header<H> {
    pub aggregated_proof: AggregatedProof,
    pub da_headers: Vec<H>,
}