Add support for standardizable SQL tasks

[weaverba137]

This PR adds support for some standardizable SQL tasks:

• Create indexes on a column or a group of columns.
• Create q3c index on columns corresponding to RA, Dec.
• Create a primary key on a table that doesn't already have one, which is a common occurrence when ingesting a new table.

There are other possible standardizable SQL tasks of course, e.g.:

• Setting permissions.
• Creating a schema.
• Truncating a table to reload it.

The intention of this PR is to create a framework for adding these additional tasks in later PRs.

@jacquesalice if you have suggestions about how to modify the index creation for tablespaces, please comment. I've seen the documentation on Confluence, so I know the syntax, but we might need to compile a list of available tablespaces and determine, do the tablespaces have the same naming convention on all servers?

[weaverba137]

@rnikutta, @jacquesalice I have created a new ticket #6 to discuss supporting tablespaces independently of this PR. Therefore I suggest merging this without doing additional work on tablespaces right now.