Reindex SKU(s) Feature

[bsuravech]

Summary
Backport the M2 feature for Reindexing Product SKUs in admin. Changes to match:
algolia/algoliasearch-magento-2#536

Result

• Adding new admin menu section for Algolia Search under System to include quick link to Algolia's system configuration section and to the reindex SKU(s) feature.
• Adminhtml controller directory Algoliasearch has been added for proper url structure and in result updated queue controller links for notifications.
• ACL has been added for Reindex SKU feature.
• Created new exception classes to match M2 with update to UnknownSkuException to ProductUnknownSkuException naming.
• Updated reindexPostAction logic to load collection instead of loading products individually as best practice for optimisation.
• Updated parameter $skus filter to preg_split array_map('trim') array_filter (to knock out spacing and blank entries)
• Updated ProductNotVisibleException catch to not retry parent product in the catch handle but on the checkAndReindex() method to retry there (this is to prevent Exception Inception where if the parent product threw an error it won't throw a fatal error within the Exception catch)
• Added and updated canProductBeReindexed method in data helper to match M1 products requirements.

[JanPetr]

Awesome job, @bsuravech! 🚀 I added few tiny comments, what you think of that?

[JanPetr]

LGTM 🚀