fix: disallow access into ws interceptors

[bbortt]

problem; access to interceptors list is exposed to public. modifications to it won't be propagated to the underlying web service template.

I personally find this a bit irritating. I think the acessor methods could be used instead, that's what this PR would change.

see this (unchanged) setter implementation:

    public void setInterceptors(List<ClientInterceptor> interceptors) {
        this.interceptors = interceptors;
        getWebServiceTemplate().setInterceptors(interceptors.toArray(new ClientInterceptor[0]));
    }

[christophd]

could you please elaborate why this has been an issue, thx

[bbortt]

could you please elaborate why this has been an issue, thx

@christophd updated the PR description.