Provide convenient way to run bats tests locally

Clarification and motivation

We currently have 4 bats scripts in the repository:

• scripts/test-binaries.bats
• scripts/test-docker.bats
• scripts/test-encoding.bats
• scripts/test-morley-client.bats

all of which are used by the CI for tests.

However at the moment it's quite inconvenient to run these locally as there are options that need to be provided (e.g. env variable that need to be set, binaries that need to be compiled, paths given, etc.) before these can be executed and there is no single place documenting all of them.

We should provide an easier method to run these locally.

I suggest adding make targets for each, with options that (where possible) have default values.

Acceptance criteria

There is a convenient way to run test bats scripts locally.

Ideally, it should be possible to run each with a single command when default options are used.