Build librocksdb 8.1.1 as part of the rocksdb-ruby gem

[johnny-lai]

Changes include:

• Switching to Github Actions from Travis
• Builds librocksdb 8.1.1 with the rocksdb-ruby gem
• During gem installation, librocksdb 8.1.1 is downloaded, built as a static library, and deleted after the RocksDB.so/RocksDB.bundle needed for the client is built

Advantages of building librocksdb as part of the gem

• Ensures rocksdb-ruby client matches a compatible librocksdb
• If there are multiple rocksdb-ruby gems installed from different versions, they can co-exist peacefully

Disadvantages:

• Long gem installation times

[johnny-lai]

I don't see the Github Actions running against this PR. Perhaps it needs to be enabled on the repository? If you want an example of what it looks like, you can take a look at https://github.com/johnny-lai/rocksdb-ruby/pull/1 https://github.com/johnny-lai/rocksdb-ruby/actions/runs/5340814651

[isamu]

Thank you for very good suggestion.

I believe Github Acitons are done after pulling in the PR. If it is not executed, review the settings here.