fix: Endpoint configuration should also accept expressions

[bakjos]

Many thanks for submitting your Pull Request ❤️!

What this PR does / why we need it:

According to the Spec the URI of the Endpoint Configuration can be a template or an expression, when using expressions, the parsing is failing

{
          "title": "EndpointConfiguration",
          "type": "object",
          "unevaluatedProperties": false,
          "properties": {
            "uri": {
              "title": "EndpointUri",
              "description": "The endpoint's URI.",
              "oneOf": [
                {
                  "title": "LiteralEndpointURI",
                  "description": "The literal endpoint's URI.",
                  "$ref": "#/$defs/uriTemplate"
                },
                {
                  "title": "ExpressionEndpointURI",
                  "$ref": "#/$defs/runtimeExpression",
                  "description": "An expression based endpoint's URI."
                }
              ]
            },
            "authentication": {
              "$ref": "#/$defs/referenceableAuthenticationPolicy",
              "title": "EndpointAuthentication",
              "description": "The authentication policy to use."
            }
          },
          "required": [
            "uri"
          ]
        }

Special notes for reviewers:

Additional information (if needed):

[ricardozanini]

I'll take a look on this, thanks for the PR!

[ricardozanini]

@bakjos I've just merged the implementation PR, which I think addresses this issue. Do you mind rebasing it?