feat(core): add API for partially config Amplify

[5d]

Description of changes

• add a new API updateConfig for customer to partialy config Amplify.

Issue #, if available

The current Amplify.configure replaces the whole configuration. If a customer wants to update a field in the configuration. The API requires a replacement at each level.

For instance, if customer has Pinpoint configured for Analytics. They wants to update the bufferSize option. They will need to do this:

import { Amplify } from 'aws-amplify';

Amplify.configure({
  ...Amplify.getConfig(),
  Analytics: {
    ...Amplify.getConfig().Analytics,
    Pinpoint: {
      ...Amplify.getConfig().Analytics?.Pinpoint!,
      bufferSize: 2000,
    }
  }
});

With this new API, customer can do:

import { Amplify } from 'aws-amplify';

Amplify.updateConfig(
  (config) => config.atKey('Analytics').atKey('Pinpoint').atKey('bufferSize'),
  2000
);

Description of how you validated changes

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[RichiCoder1]

I randomly stumbled up on this PR and wanted to toss out this might be a good use case for Immer: https://immerjs.github.io/immer/produce