cluster: cass_cluster_set_tcp_keepalive

[muzarski]

Implementation of cass_cluster_set_tcp_keepalive. In cpp-driver, by default, this is disabled - same is true for rust-driver.

Pre-review checklist

• [x] I have split my patch into logically separate commits.
• [x] All commit messages clearly explain what they change and why.
• [x] PR description sums up the changes and reasons why they should be introduced.
• ~[ ] I have enabled appropriate tests in .github/workflows/build.yml in gtest_filter.~
• ~[ ] I have enabled appropriate tests in .github/workflows/cassandra.yml in gtest_filter.~