Add support for specifying custom `:meta` options.

[smoothcontract]

What does this PR do?

• Currently the pagination implementation completely overwrites the response :meta options - I have a use case that requires adding additional options to the meta section but the gem doesn't support that. This change allows something like the following to work as expected:

paginate my_collection, meta: { foo: 'bar' }

...and will include the specified custom metadata in addition to the pagination metadata.