Build AWSectionStore class, a storage abstraction layer to support persistence and retrieval of:

• AWSection obejcts (section_qid, topic_qid, locale, etc...): pre-generated and stored AW article sections
• (maybe) AWArticleMetadata objects (created and updated timestamp, section ids and section order... ): this is globally reachable metadata without needing network-trips

Proposed interface:

• getSection( topic_qid, section_qid, locale, … ): AWSection
• getSectionsForTopic( topic_qid, locale, … ): AWSection
• setSection( AWSection, … ): bool
• deleteSection( topic_qid, section_qid, locale, … )
• getArticleMetadata( topic_qid, … ): AWArticleMetadata
• setArticleMetadata( AWArticleMetadata, … ): bool
• static createMissingSectionBlock( topic_qid, section_qid, locale, … ): AWSection

Goals:

• This abstraction is independent to the specific storage backend, to be decided on T422620: Agree with stakeholders on the substrate nature, location, and access method
• Storage backend should be configurable and transparently usable in non-production environments (DB and provided schema)