Print undocumented functions to console while generating docs

[alamb]

Which issue does this PR close?

Part of #12740

First part of #12872

Rationale for this change

Eventually I would like to ensure that all functions have documentation. Now that we have the automated documentation builder in place, it is possible to see what is missing.

What changes are included in this PR?

As first step, update the print docs script to print out the list of functions that are not documented. As a follow on PR I will make this an error once we have all functions documented

Are these changes tested?

I tested them manually. Here is what it looks like:

INFO: The following functions do not have documentation:
  - regr_avgy
  - regr_sxx
  - regr_slope
  - regr_r2
  - regr_count
  - regr_avgx
  - regr_syy
  - regr_intercept
  - regr_sxy
...

Here is what it looked like before

(venv) andrewlamb@Andrews-MacBook-Pro-2:~/Software/datafusion$ ./dev/update_function_docs.sh
/Users/andrewlamb/Software/datafusion
Inserting header
Running CLI and inserting aggregate function docs table
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.10s
     Running `target/debug/print_functions_docs aggregate`
Running prettier
docs/source/user-guide/sql/aggregate_functions_new.md 58ms
'docs/source/user-guide/sql/aggregate_functions_new.md' successfully updated!
Inserting header
Running CLI and inserting scalar function docs table
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/print_functions_docs scalar`
Running prettier
docs/source/user-guide/sql/scalar_functions_new.md 93ms
'docs/source/user-guide/sql/scalar_functions_new.md' successfully updated!
Inserting header
Running CLI and inserting window function docs table
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/print_functions_docs window`
Running prettier
docs/source/user-guide/sql/window_functions_new.md 23ms
'docs/source/user-guide/sql/window_functions_new.md' successfully updated!

Are there any user-facing changes?

[alamb]

FYI @Omega359 and @jonathanc-n

[Omega359]

LGTM - thanks @alamb

[jonathanc-n]

this LGTM thanks for the help @alamb

[comphead]

lgtm thanks @alamb

[alamb]

Thank you everyone for the review