[@aws-cdk/pipelines] Allow multiple build / install commands for SimpleSynthAction

[timbaer]

I think the buildspec generation in the SimpleSynthAction can be improved. For cases where you need run additional build-commands (e.g. build lambda-sources before synth), it would be good to have a way to pass multiple install and build commands to the SimpleSynthAction. A good way would be to provide a string-array for parameter SimpleSynthAction.buildCommand and SimpleSynthAction.installCommand.

Currently, I'm helping myself by concatenating all install/build commands as follows:

SimpleSynthAction.standardNpmSynth({
                sourceArtifact,
                cloudAssemblyArtifact,
                installCommand: 'npm ci --prefix ../lambda/create' +
                    '&& npm ci --prefix ../lambda/update' +
                    '&& npm ci',
                buildCommand: 'npm run build --prefix ../lambda/create' +
                    '&& npm run build --prefix ../lambda/update' +
                    '&& npm run build'
            }

Use Case

As a cdk-pipeline user, I want to pass a list of build-commands / actions to the build action of a pipeline to run them one after another or in parallel.

Proposed Solution

1. change parameter-type of buildCommand and installCommand from string to Array

• ⚠️ This feature might incur a breaking change

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This is a 🚀 Feature Request

[asterikx]

Similar to #9021