fix: Fix publickey encoding && Add assertionMethod

[DaevMithran]

Signed-off-by: DaevMithran daevmithran1999@gmail.com

This pull request

• Adds an assertionMethod in the didDocument
• encodes the publicKey using MULTICODEC_ED25519_PUB_HEADER = new Uint8Array([0xed, 0x01]) which is followed in did:key spec, and the signature suites for publicKeyMultibase BREAKING CHANGE: This will need changes in cheqd/node

Both the changes were needed to support JSONLD credentials.

References

• https://w3c-ccg.github.io/did-method-key/#derive-encryption-key-algorithm
• Should this library throw errors defined in the did:key spec? digitalbazaar/ed25519-verification-key-2020#18

[Eengineer1]

@DaevMithran Thanks for pointing out.
This PR is needed right after switching to header prefix ledger-side as well.
Till then, let's focus on overriding the Veramo signer.

Closing this, as there will be many extensive changes needed in the SDK signing as well, not only those present here.

Let me know your thoughts.

[DaevMithran]

@Eengineer1 Can you please point out the code where we need to change the SDK's signing logic. I think there's no need for that.

• Other than that I can create a separate PR for adding assertion method in the didDoc