[LIQ] Extend with group by and having with aggregators (#1843)

* [LIQ] Extend with `group by` and `having` support

Also update documentation with extensive examples and add some parser
tests.

Note: `make generate` JS files included.

Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>

* Merge `liq-add-support-for-aggregators` branch

Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>

* Fix link, remove `_` example

Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>

* Wrap example LIQ queries inside `query [[ .. ]]` and replace `sql` code block type to `lua`

Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>

* Example self-consistency fix

Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>

* Fixed some queries

* Add experimental tags to LIQ aggregation/grouping

---------

Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>
Co-authored-by: Zef Hemel <zef@zef.me>

client/space_lua/parse-lua.terms.js

@@ -22,15 +22,17 @@ export const
   OrderBy = 70,
   SelectClause = 72,
   LimitClause = 74,
-  IfStatement = 79,
-  ForStatement = 84,
-  ForNumeric = 86,
-  ForGeneric = 87,
-  NameList = 88,
-  ExpList = 90,
-  FuncName = 92,
-  VarList = 96,
-  AttNameList = 98,
-  AttName = 99,
-  Attrib = 100,
-  ReturnStatement = 101
+  GroupByClause = 76,
+  HavingClause = 78,
+  IfStatement = 83,
+  ForStatement = 88,
+  ForNumeric = 90,
+  ForGeneric = 91,
+  NameList = 92,
+  ExpList = 94,
+  FuncName = 96,
+  VarList = 100,
+  AttNameList = 102,
+  AttName = 103,
+  Attrib = 104,
+  ReturnStatement = 105