Support custom public certificates

[vzhukovs]

This changes proposal adds an ability to provide custom certificates.
There is a new field in api configuration, called publicCrtPath, which represents a simple directory on file system, where certificates *.crt are located. All those certificates take into account during user requests.

export interface IRestAPIConfig {
    baseUrl?: string;
    headers?: any;
    // path to self signed certificate
    ssCrtPath?: string;
    // path to public certificates
>>    publicCrtPath?: string;
    loggingEnabled?: boolean;
    machineToken?: string;
    userToken?: string;
}

Issue: eclipse-che/che#17440

Signed-off-by: Vladyslav Zhukovskyi vzhukovs@redhat.com