Calculate CRC32 checksums of persisted build trace chunks

What does this MR do?

This merge request aims to make Cloud Native Build Logs more resilient by calculating CRC32 checksums of chunks that are about to get persisted in a permanent storage.

Migration

Up:

== 20200818092401 AddChecksumToBuildChunk: migrating ==========================
-- add_column(:ci_build_trace_chunks, :checksum, :binary)
   -> 0.0009s
== 20200818092401 AddChecksumToBuildChunk: migrated (0.0010s) =================

Down:

== 20200818092401 AddChecksumToBuildChunk: reverting ==========================
-- remove_column(:ci_build_trace_chunks, :checksum, :binary)
   -> 0.0015s
== 20200818092401 AddChecksumToBuildChunk: reverted (0.0040s) =================

Conformity

• Changelog entry
• Code review guidelines

Issues

Closes #230944 (closed)
Closes #241490 (closed)