Add `searchDatabases` to `IBaseQueries`

[ultram4rine]

Is your feature request related to a problem? Please describe.
Hi! I noticed that extension is trying to search databases on completions.

vscode-sqltools/packages/plugins/intellisense/language-server.ts

Line 59 in c825e14

const dbs = await conn.searchItems(ContextValue.DATABASE, currentWord) as [NSDatabase.IDatabase];

However, at least default drivers doesn't support searching databases, i.e. PG:

vscode-sqltools/packages/driver.pg/src/ls/driver.ts

Lines 229 to 236 in c825e14

	public searchItems(itemType: ContextValue, search: string, extraParams: any = {}): Promise<NSDatabase.SearchableItem[]> {
	switch (itemType) {
	case ContextValue.TABLE:
	return this.queryResults(this.queries.searchTables({ search }));
	case ContextValue.COLUMN:
	return this.queryResults(this.queries.searchColumns({ search, ...extraParams }));
	}
	}

So, if implement route for searching databases, feature should work. Example: ultram4rine/sqltools-clickhouse-driver#683. But I didn't found searchDatabases method in base queries interface.

Describe the solution you'd like
Maybe add method to IBaseQueries for clarity?

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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