support/datastore: Add CRC32C validation when exporting and consuming tx meta files

[tamirms]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with name of package that is most changed in the PR, ex.
  services/friendbot, or all or doc if the changes are broad or impact many
  packages.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md
  files, etc... affected by this change). Take a look in the docs folder for a given service,
  like this one.

Release planning

• I've updated the relevant CHANGELOG (here for Horizon) if
  needed with deprecations, added features, breaking changes, and DB schema changes.
• I've decided if this PR requires a new major/minor version according to
  semver, or if it's mainly a patch change. The PR is targeted at the next
  release branch if it's not a patch change.

What

Add CRC32C validation validation when uploading and downloading tx meta files.

https://stellarorg.atlassian.net/browse/HUBBLE-271
https://stellarorg.atlassian.net/browse/HUBBLE-278

Why

From https://cloud.google.com/storage/docs/hashes-etags

There are a variety of ways that data can be corrupted while uploading to or downloading from the Cloud:

• Memory errors on client or server computers, or routers along the path
• Software bugs (e.g., in a library that customers use)
• Changes to the source file when an upload occurs over an extended period of time

Cloud Storage supports two types of hashes you can use to check the integrity of your data: CRC32C and MD5. CRC32C is the recommended validation method for performing integrity checks.

Known limitations

Unfortunately, the CRC32 hash must be computed at the beginning of the HTTP request which means we must write out the payload to a temporary buffer instead of computing the hash on the fly.

[sreuland]

@tamirms , I made small edit on description, I think the intention was to reference HUBBLE-278 for crc check.

[tamirms]

@sreuland my bad, thanks for correcting the mistake!