fix: OpenAPI generator config - protected keyword

[petermetz]

Describe the bug

We are not compliant with the RFC 7515 spec when it comes to our generated models.

Currently our OpenAPI spec generation has an issue with the models defined for representing RFC 7515 JSON Web Signatures 1 with the field protected being mangled by the OpenAPI generator because protected is a soft reserved keyword in Typescript.
Since protected is only a softly reserved keyword, this means that you can still declare classes/interfaces with fields that are called protected which is what we need since the RFC mentioned above declares exactly that for JWS recipients.

To Reproduce

Build the project and observe that the generated code looks like this:

/**
 * A JSON Web Signature. See: https://tools.ietf.org/html/rfc7515 for info about standard.
 * @export
 * @interface JWSRecipient
 */
export interface JWSRecipient {
    /**
     * 
     * @type {string}
     * @memberof JWSRecipient
     */
    signature: string;
    /**
     * 
     * @type {string}
     * @memberof JWSRecipient
     */
    _protected?: string;
    /**
     * 
     * @type {{ [key: string]: object; }}
     * @memberof JWSRecipient
     */
    header?: { [key: string]: object; };
}

Expected behavior

The generated code should look like this:

/**
 * A JSON Web Signature. See: https://tools.ietf.org/html/rfc7515 for info about standard.
 * @export
 * @interface JWSRecipient
 */
export interface JWSRecipient {
    /**
     * 
     * @type {string}
     * @memberof JWSRecipient
     */
    signature: string;
    /**
     * 
     * @type {string}
     * @memberof JWSRecipient
     */
    protected?: string;
    /**
     * 
     * @type {{ [key: string]: object; }}
     * @memberof JWSRecipient
     */
    header?: { [key: string]: object; };
}

Cloud provider or hardware configuration:

Dev machine

Operating system name, version, build:

Linux 5.4.0-58-generic x86_64
NAME="Ubuntu"
VERSION="20.04.1 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.1 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal

Hyperledger Cactus release version or commit (git rev-parse --short HEAD):

v0.2.0

Hyperledger Cactus Plugins/Connectors Used

N/A

Additional context

OpenAPITools/openapi-generator#7100 (comment)

cc: @takeutak @sfuji822 @hartm @jonathan-m-hamilton