Explicit support for API key authentication

[parkerduckworth]

Example:

import weaviate from 'weaviate-ts-client';

const client = weaviate.client({
  scheme: 'http',
  host: 'localhost:8080',
  apiKey: new weaviate.ApiKey('my-secret-key'),
});

await client.misc.metaGetter().do();

Closes #6

[bobvanluijt]

Following to see when it's merged