Generates a markdown representation of the schema for all keyspaces and tables
within the CassandraDatabase instance. This method utilizes the
format_keyspace_to_markdown method to create markdown sections for each
keyspace, assembling them into a comprehensive schema document.
Iterates through each keyspace in the database, utilizing
format_keyspace_to_markdown to generate markdown for each keyspace's schema,
including details of its tables. These sections are concatenated to form a
single markdown document that represents the schema of the entire database or
the subset of keyspaces that have been resolved in this instance.
