EWC RFC 001: Update images for authorisation code flow

[georgepadayatti]

Excerpt from https://github.com/EWC-consortium/eudi-wallet-rfcs/pull/4: The figure does not seem to implement the authorization code flow, as it starts with a credential offer, while the auth code flow assumes the wallet already knows the issuer and requests its metadata.

Reference is given below:

https://github.com/EWC-consortium/eudi-wallet-rfcs/blob/3a093511e9c735319ab0b3285e92fc7a75896872/ewc-rfc001-issue-verifiable-credential.md?plain=1#L59-L61

[georgepadayatti]

@lalc Should we use mermaid diagrams to create it programmatically ? GitHub has native mermaid support. An example is given below:

  graph TD;
      A-->B;
      A-->C;
      B-->D;
      C-->D;