feat(core): improved API for tags

[iamhopaul123]

Improved tagging API.

Please read the contribution guidelines and follow the pull-request checklist.

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

[eladb]

I've updated the title. Even if this is only a design, you'll eventually evolve it to the actual PR. Please update PR description

[iamhopaul123]

I've updated the title. Even if this is only a design, you'll eventually evolve it to the actual PR. Please update PR description

But I've submitted another PR for the implementation part. Do I need to close that PR and migrate those changes to this PR?

[eladb]

@moofish32 what do you think?

[eladb]

since tags are essentially maps, why not something like this:

Tag.add(scope, { sfoo: 'bar' })

This will allow people to add multiple tags like this:

Tag.add(scope, {
  tag1: 'value1',
  tag2: 'value2'
});

[iamhopaul123]

But tag also supports other properties like priority. See here. I would suggest Tag.add(scope, [
(tag1, 'value1', props)
(tag2, 'value2', props)
]);
but not sure if that's an over-engineer.

[eladb]

okay, let's just leave it with Tag.add(scope, key, value[, options)

[eladb]

Missing unit test

[eladb]

@iamhopaul123 could you please also submit a PR to update the developer guide:
https://github.com/awsdocs/aws-cdk-guide/blob/master/doc_source/tagging.md