Renaming to prepare for proc/function support for Pg

[gledis69]

Why make this change?

Postgres stored procedures and function are very similar in the way they are defined. The differences as far as our application are concerned are:

• procedures don't return any data, only functions can return data, but functions can return void as well.
• procedures are called as CALL <procedure_name>, while functions are called as SELECT * FROM <function_name> or SELECT <function_name>.

Due to these small differences procedures and functions for pg can be handled the same for the most part in our engine so this PR generalizes the nomenclature of any StoredProcedure related structure to DatabaseExecutable to imply both stored procedures and functions. I imagine this will be useful for MsSql and MySql as well when they add function support.

This PR is a prerequisite for a subsequent PR which will add procedure/function support for PG, but I figured this can be reviewed and merged separately since reviewing the proc/func support PR would become too hard due to all the refactoring.

What is this change?

• Mostly renaming classes, functions, variables which include StoredProcedure to smth more generic DatabaseExecutable.
• Updating comments to reflect the refactoring.

How was this tested?

• The CI tests will validate that the refactoring didn't break any of our existing tests

Sample Request(s)

N/A

[abhishekkumams]

I think once all the conflicts are resolved, it would be easier to review.

Need more time to review, given the new function source type.

[seantleonard]

There have been many changes since this was opened. Closing for now and you can re-open with latest changes and conflicts resolve.