[11.9] Add support for Advanced Search API

[IAL32]

The Advanced Search API can be called as follows:

(GET) /search

Attribute	Type	Required	Description
scope	string	yes	The scope to search in
search	string	yes	The search query
state	string	no	Filter by state. Issues and merge requests are supported; it is ignored for other scopes.
confidential	boolean	no	Filter by confidentiality. Issues scope is supported; it is ignored for other scopes.
order_by	string	no	Allowed values are created_at only. If this is not set, the results are either sorted by created_at in descending order for basic search, or by the most relevant documents when using advanced search.
sort	string	no	Allowed values are asc or desc only. If this is not set, the results are either sorted by created_at in descending order for basic search, or by the most relevant documents when using advanced search.

This PR adds support for this API.

[stale[bot]]

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