services/horizon/internal/db2/schema/migrations: Add constraints on database columns which cannot hold negative values

[tamirms]

…values

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

Fixes #2605

Add constraints on database columns which can only hold non-negative values.

verify-range tests revealed a bug in which max_fee value of this transaction has overflowed. This happened because the type of this field in XDR Transaction struct definition was (before fee bump changes) uint32 but Postgres does not support unsigned integer types.

To catch this kind of errors faster we should add constraints to fields like max_fee. While this can stop ingestion on invalid value insert attempt it's safer.