Add explain plans for ClickBench queries (#20666)

## Which issue does this PR close?

- Part of #18489 
- Related to #20180

## Rationale for this change

This looks like a monster PR but I think it will be quite easy to review
(it just adds some new `EXPLAIN` tests). If it would be helpful I can
break it into smaller pieces

I want to improve the plans for ClickBench Query 29

However, the plans for the ClickBench queries are not in our tests
anywhere (so when I make the improvements in
#20665 no explain plan tests
change)

So to start, let's start with adding the explain plans for all the
queries in clickbench.slt to so it is clear what our current plans look
like as well as to make it clear what the change of plans are

## What changes are included in this PR?

Add explain plans to some .slt tests

## Are these changes tested?

Only tests

## Are there any user-facing changes?
No, this only adds tests

Author: alamb