[Synthetic-job-manager]: ✨ Allow the user to customize Node & Browser cronjob schedule value

[yvann-ponce]

Which issue this PR fixes

#2171

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• Chart Version bumped
• Variables are documented in the README.md
• Title of the PR starts with chart name (e.g. [mychartname])

🚀 feat(Synthetic-job-manager): Add customisation for Node & Browser cronjob schedule value

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