Adds migrations for page events columns

[manuelurenah]

Description

• Adds page events columns (publishedAt, republishedAt, archivedAt and unpublishedAt) to the public pages table in postgres
• Adds migration script to populate these values from previous entries
• Modifies putMeta method to send the data when meta is modified
• This is part of Additional Columns #33

QA

In order to be able to test this feature, you should link this package and #49 in a clay project. I've been using https://github.com/clay/clay-starter to develop this feature, that's a good starting point.

Testing steps

1. Go inside a clay project directory (i.e.: clay-starter)
2. Spin up an instance of clay with make
3. Open another terminal window or tab and make sure adminer is up and running using docker-compose up -d adminer
4. Bootstrap the starter data with make bootstrap (where the Makefile is located)
5. Make your way into the app directory (or where the package.json file is located) and link the previously mentioned packages with npm link amphora-storage-postgres (make sure the packages are in the correct branch and linked)
6. Restart the clay instance with rs. After it's done, you should see a message stating Migrations Complete
7. Go into http://localhost:8080 and login the db (system, server, username and database are all postgres; password is example)
8. Check that the schema of the pages table have the following columns: published_at, unpublished_at, archive_at and republished_at
9. You should be able to see in the pages table entries with all the previous columns plus the new ones.
10. You should be able to update, publish, archive and everything else without any problems

[pedro-rosario]

You could abstract this logic into a small function

Suggested change

	const latestUnpublish = parsedValue.history
	const latestUnpublish = getLatestActionByName(parsedValue.history, 'unpublish'),
	latestArchived = getLatestActionByName(parsedValue.history, 'archive')

function getLatestActionByName(history = [], action) {
  return history
    .filter(event => event.action === action)
    .pop() || {};
}

[pedro-rosario]

Suggested change

	* @param {String} action
	* @param {string} action

[manuelurenah]

Convention is to have String capitalize