GoCQL drop-in replacement

The goal of this pull request is to provide a gocql module inside the scylla-go-driver repository that could be used as a drop-in
replacement for gocql, just by using a replace directive in go.mod like this:
replace github.com/gocql/gocql => github.com/scylladb/scylla-go-driver/gocql <version/commit>

Benefits

Features: ORM, query building and migrations support can be used just by replacing GoCQL with the new driver in https://github.com/scylladb/gocqlx
Tests: Existing integration tests for GoCQLX, Scylla Manager, Scylla Operator, etc. can be used to test drivers correctness and safety.

Tests

New gocql package was tested against GocqlX and Scylla Manager tests.
GocqlX and Scylla Manager tests pass with exceptions:

• Scylla Manager repair & backup integration tests.
• GocqlX schemagen - due to metadata inconsistencies in scylladb/gocql metadata_scylla.go and metadata_cassandra.go
  I added a workflow to run the already passed tests on GitHub Actions, if you want to run them please refer to this action.

To pass the Scylla Manager tests its also needed to add two lines of code to the manager tests as gocql and the new driver return different error messages on unauthorised errors.

Changes

This PR makes many small changes mostly to the driver's API so it can provide a gocql compatible API in the gocql package,
those chages include:

• Allowing to check if session is closed
• Allowing per-query retry policy setting
• More getters/setters for Query and Iter
• Configuring coalescing wait time
• Transforming a query to a prepared one straight from query level
• Allowing binding query arguments using Serializable interface
• Exporting UDT fields in frame package
• Falling back to random shard discovery when shard-aware port is missing/misbehaving

gocql package

This PR features a new gocql package, wrapping Session, Query and Iter in structs exporting gocql API methods.
Base functionality is here, some missing gocql features are:

• Conviction policy
• Client-side timeouts
• HostDialer
• Observers
• Address Translation
• Tracer