To avoid having to specify each spec by hand (which can miss specs to be
added), the test infrastructure now performs classpath discovery so that
each spec added, is automatically considered.
Relates #40358
* Added Limitations page
* Made the aggregations page follow the common template for functions
* Modified all tables to have the first row's cells content centered
* Polishing in other various sections
Add GREATEST(expr1, expr2, ... exprN) and LEAST(expr1, expr2, exprN)
functions which are in the family of CONDITIONAL functions.
Implementation follows PostgreSQL behaviour, so the functions return
`NULL` when all of their arguments evaluate to `NULL`.
Renamed `CoalescePipe` and `CoalesceProcessor` to `ConditionalPipe` and
`ConditionalProcessor` respectively, to be able to reuse them for
`Greatest` and `Least` evaluations. To achieve that `ConditionalOperation`
has been added to differentiate between the functionalities at execution
time.
Closes: #35878
