Fix locale alias by including locale object in MultiSite Context

[adamraya]

Description

This PR fixes the issue #712.

Problem

The MultiSite refactor to optimize Server-side performance PR #667, introduced a regression where the locale.alias defined in the sites.js configuration is no longer working.

Solution

The implemented solution follows the proposed solution in the issue #712.
The MultiSiteContext now includes the locale object including the locale.id and locale.alias and uses the locale.alias in URLs over the locale.id if the locale.alias is defined in sites.js configuration.

Types of Changes

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Documentation update
• Breaking change (could cause existing functionality to not work as expected)
• Other changes (non-breaking changes that does not fit any of the above)

Breaking changes include:

• Removing a public function or component or prop
• Adding a required argument to a function
• Changing the data type of a function parameter or return value
• Adding a new peer dependency to package.json

Changes

• MultiSiteContext includes the locale object.
• Fixed tests to work with the locale object.
• Small refactor to re-use code by adding the site utils getSiteByReference.

How to Test-Drive This PR

1. Add a locale.alias to the packages/template-retail-react-app/config/sites.js configuration.

E.g.

...
l10n: {
            supportedCurrencies: ['GBP', 'EUR', 'CNY', 'JPY'],
            defaultCurrency: 'GBP',
            supportedLocales: [
...
                {
                    id: 'en-GB',
                    preferredCurrency: 'GBP'
                    alias: 'TestLocaleAliasGB' // Locale alias
                },
...

2. Start the Template Retail React App in the monorepo by running npm run start.

Verify 👇

• The locale alias defined in the sites.js config file is used in the URLs (Except for the home page).
• The locale alias is used in the URL when switching locales using the Select component in the Footer.

Checklists

General

• Changes are covered by test cases
• CHANGELOG.md updated with a short description of changes (not required for documentation updates)

Accessibility Compliance

You must check off all items in one of the follow two lists:

• There are no changes to UI

or...

• Changes were tested with a Screen Reader (iOS VoiceOver or Android Talkback) and had no issues
• Changes comply with WCAG 2.0 guidelines levels A and AA
• Changes to common UI patterns and interactions comply with WAI-ARIA best practices

Localization

• Changes include a UI text update in the Retail React App (which requires translation)