Add ostruct as an explicit dependency

[RemoteCTO]

This gem makes use of OpenStruct however this appears to be steadily being removed by default over time:

• Remove usage of OpenStruct or add ostruct as dependency  mileszs/wicked_pdf#1116
• Warn ostruct as bundled gems for Ruby 3.5 ruby/ruby#10428
• ruby 3.4.0dev deprecates OpenStruct rails/jbuilder#561

Without OpenStruct on the system it causes the errors when running migrations:

bin/rails aborted!
NameError: uninitialized constant Timescaledb::Connection::OpenStruct (NameError)

      query.map(&OpenStruct.method(:new))
                 ^^^^^^^^^^

Tasks: TOP => db:schema:dump

Ideally the implementation would be changed to switch OpenStruct with Struct, but this patches breakages in the meantime.

[CLAassistant]

All committers have signed the CLA.

[jonatas]

Thanks for bringing this improvement @RemoteCTO, I'll check it soon. As it depends on activesupport I was expecting it was not necessary, but that's a good call to make the dependencies clean!