Add ECDSA support and fixed DID resolution for hosted public keys

[rubenroblesl]

Introduced support for ECDSA (ES256) signature verification and improved DID resolution process for better compatibility with web-hosted DID documents.

Changes include:

ExternalProofProbe.java

• Added support for ECDSA (ES256) in addition to RSA (RS256) when validating JWT signatures.
• Replaced usage of the default ConfigurableDocumentLoader.DOCUMENT_LOADER with new CachingDocumentLoader() to ensure enableHttp, enableHttps, and enableFile flags are correctly enabled by default.

SimpleDidResolver.java

• Fixed the .well-known DID resolution path by correcting the variable assignment (from /well-known to ./well-known) as specified in the VC Data Model spec.
• Replaced uri.getPath() == null with a check for an empty string (.isEmpty()), since getPath() never returns null.
• Modified the logic when extracting the public key from a DID document:
  • Previously, publicKeyMultibase was required and would throw if missing.
  • Now, both publicKeyJwk and publicKeyMultibase are handled conditionally:
    • If publicKeyJwk is present, it is parsed and used.
    • If publicKeyMultibase is present, it is used instead.
  • This provides compatibility with DID documents using either key representation format, as permitted by the spec.

[rubenroblesl]

@xaviaracil Hi, I'd appreciate If you could review my pull request to the project. Greetings.