Altme/Talao simplifications regarding SSI options

[ThierryThevenet]

As we create a new wallet app for EUDI , there are simplifications to remove the management of keys requested for the EUDI wallet but useless for SSI wallets . These keys cause complex treatments and are the root of many bugs we experience :

1. Use only client_id scheme DIDs. It means that the client_id of the wallet is always a DID. remove the switch and logic to change the client id scheme
2. Remove the options to use a confidential client as the client_id is always a DID. remove the switch and imput fields
3. Keep the wallet attestation specific key as an independant JWK. Bearing in mind that that key is never used for a client_id and in a proof of key ownership for VC. The wallet attestation is only used to authenticate the wallet with the authorization server if the client authentication method is client attestation (needed for authorization endpoint, PAR endpoint, token endpoint)
4. Use Proof of possession Header only with kid as kid is a DID + fragment and jwk is no more used for VC