feat: Add metadata field on the certificate

[goran-ethernal]

Description

Metadata field

This PR adds a Metadata field to certificate. This field is a Hash field, that different chains can use to store arbitrary data relevant to them. In our case, we store the the number of block on L2 until which we built the given certificate.

For example, we built a certificate for blocks 10 to 20 on L2. We will store number 20 in a form of hash to the Metadata field on the certificate.

Once the agglayer team introduces the rpc endpoint to get the last sent certificate by our network, we can use that field to know from which block to build the next certificate. For now, we use a local database on the aggsender for this, but we want to avoid cases where we might lose our local db, or it gets corrupted, or we missed a lot of blocks.

Invalid signer issue

This PR also fixes the issue of signing a wrong certificate hash, which caused the InvalidSigner problem on the agglayer.
agglayer signs the same data as in HashToSign function.

Global index on imported bridge exits is first converted to little endian slice, and then hashed, as per agglayer code.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud