Insert project filters into OxQL query AST instead of raw string

[david-crespo]

Closes #7532. Instead of manipulating the query as a string to add the filters at the end, pass the silo and project IDs to the oximeter client, which has the parsed query AST on hand, and let it do the manipulation.

In case of simple queries, we just insert the filters after the initial get operation. For "grouped" queries (like { get a:b; get c:d | filter timestamp > @now() } | filter x > y), the query is a tree, so we recurse down it and insert the filters in every leaf node, which is a simple query.

[bnaecker]

This looks great, thanks for doing it! I agree we should deduplicate the actual query-running method, but otherwise looks good. Thanks for the tests too.

[bnaecker]

Looks great, thanks!