Search component

[Etsija]

This PR introduces a new component "search", which is implemented with the sliced architecture. Initial implementation for the service and endpoint returns a list of all ORT run ids which include a given ORT ID. The service can later on be extended to other search functionality, for example to provide all products/repositories that are affected by a given vulnerability.

Details:

• so far, only ORT IDs are used for searching. PURL implementation (taking into account curated PURLs) will later on extend this
• the search can be scoped to a specific organization, organization+product, or organization+product+repository
• scoping parameters are validated (eg. there can be no search with productId but without a given organizationId
• the search is regEx based, so for example substring of a package ID can be used

Please see the commits for details.

[Etsija]

NOTE: as decided in today's ORT Server Community Meeting, this PR will stay on hold until after the new authorization concept is fully merged (it needs then some changes to permissions handling and filtering the search results). Meanwhile, I am still open to general review comments regarding my PR.

[sschuberth]

I believe that ignoring a "docs" directory is too generic.

[Etsija]

That .gitignore change is old anyway, so I will remove the corr. documents and remove the commit.