feat(templating): adds encodeBase64 handlebars helper

[moltar]

Changes

Adds a encodeBase64 handlebars helper that encodes a string to Base64.

Context

When using template variables with strings that may contain special characters, it makes it more
difficult to use with commands.

Consider this example:

"postUpgradeTasks": [
  "echo \"{{body}}\" > file.md"
]

The value of the body variable contains the full changelog, which may contain anything.

Renovate will replace the variable, before the command runs, and thus it will result in a command:

echo "This is a changelog" > file.md

But if the body variable contains a double quote, the command will fail:

echo "This is "a" changelog" > file.md

By encoding the values in Base64, we can avoid this issue:

"postUpgradeTasks": [
  "echo \"{{encodeBase64 body}}\" | base64 -d > file.md"
]

Related discussion: #26175

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[moltar]

Added extra tests for nullish coalescing to fix coverage.

[renovate-release]

🎉 This PR is included in version 37.90.0 🎉

The release is available on:

• GitHub release
• 37.90.0

Your semantic-release bot 📦🚀