Implement a graceful container shutdown

[TrevorBenson]

Description

This PR implements a change to the buildImage for the cardano-db-sync container.

1. Uses Dockerfile instruction stopsignal to change the default SIGTERM to SIGINT
2. Uses exec so that the primary process is the cardano-db-sync binary process, instead of the bash shell script.
3. Added an entry to the CHANGELOG as checklist suggested.

Should resolve issue cardano-db-sync container doesn't gracefully shut down

Checklist

• Commit sequence broadly makes sense
• Commits have useful messages
• New tests are added if needed and existing tests are updated
• Any changes are noted in the changelog
• Code is formatted with fourmolu on version 0.10.1.0 (which can be run with scripts/fourmolize.sh)
• Self-reviewed the diff

Migrations

• The pr causes a breaking change of type a,b or c
• If there is a breaking change, the pr includes a database migration and/or a fix process for old values, so that upgrade is possible
• Resyncing and running the migrations provided will result in the same database semantically

If there is a breaking change, especially a big one, please add a justification here. Please elaborate
more what the migration achieves, what it cannot achieve or why a migration is not possible.

Additional Details / Empty Checklist Items

• New tests added or existing updated if needed. I didn't find tests specific to building the container image. I left it empty in case I overlooked something and reviewer points me at tests that require fixing.
• Code is formatted with fourmolu. PR changes nix files. The instructions for using fourmolu appeared to be a specific haskell code, so did not check this (yet).

[Cmdv]

@TrevorBenson Thanks for the PR, we're just trying to fix the CI failures which aren't actually related to this PR once those are fixed we'll be able to put this into master.

[TrevorBenson]

@TrevorBenson Thanks for the PR, we're just trying to fix the CI failures which aren't actually related to this PR once those are fixed we'll be able to put this into master.

Thanks. I took a quick look at them the other day and noticed they seemed to exist prior to this PR, so figured I could skip looking for root causes.

Glad to know I wasn't mistaken 👍🏼