Added content_metadata logic to the storage

Summary:
Keeping the indexed content_metadata in the storage with a content_metadata table.
Possibility to add with and without duplications and getting the content_metadata
with tool information.
works only for NPM context also because tool configuration.

TODO:

• add json schema in json/ (should we keep CodeMeta schema as is or put PURl to it

for the translated_metadata_property?)

Test Plan:

• content_metadata_missing
• content_metadata_add skipping duplicate
• content_metadata_add dropping duplicate
• content_metadata_get
• db_to_metadata conveter

Reviewers: ardumont

Differential Revision: https://forge.softwareheritage.org/D219