Allow to avoid certificates splitting into multiple files

[Infra-Red]

Describe the Enhancement

Currently, builpdack splits the certificate into multiple files when a .pem file contains multiple entries. I would like to introduce an option that will allow us to preserve the original .pem format and ignore splitting behavior.

Possible Solution

The proposed solution is to introduce a new environment variable BP_EMBED_CERTS_SKIP_SPLITTING which will ignore certificate splitting when supplied in the build parameters. I noticed that multi-certificates file is not supported by helper (https://github.com/paketo-buildpacks/ca-certificates/issues/100) so we can always ignore BP_EMBED_CERTS_SKIP_SPLITTING value unless BP_RUNTIME_CERT_BINDING_DISABLED is set a true value.

Motivation

In my scenario, I'm using ca-certificates buildpack to only add certificates to a layer and make them available during runtime (BP_EMBED_CERTS=true and BP_RUNTIME_CERT_BINDING_DISABLED=true) which is later specified in sslrootcert PostgreSQL connection parameters. Current splitting behavior makes it difficult to execute certificate rotation as sslrootcert accepts only a single file value so preserving multiple certificates will make it easier to perform certificate rotation.

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Please let me know if the proposed solution is fine with you. I'm going to work on PR If this is something you are ready to accept.