feat: add a smart query for tax map

[fragwuerdig]

Currently the active tax map can only be retrieved by doing a raw query on the tax_info store key (in hex: 7461785F696E666F). This is very inconvenient. A smart query is much easier to use. This involves following tasks for implementation:

• Add a tax map query type
• Add a tax map response type (or just use the TaxMap type directly as response type)
• Hook everything up in the query endpoint