Feat: support branch specific secrets

[erezrokah]

Which problem is this feature request solving?

The plugin supports CONTEXT specific secrets by setting a NETLIFY_CONTEXT tag in AWS Secrets manager.
It can be useful to add NETLIFY_BRANCH support too.

Describe the solution you'd like

If a NETLIFY_BRANCH tag is added to a secret in AWS, we should only inject that secret to the matching branch

Describe alternatives you've considered

N/A

Can you submit a pull request?

Yes

[erezrokah]

More on this, the plugin uses the CONTEXT env variable to filter secrets. It can only have 3 values: production, deploy-preview or branch-deploy.

Since context can also mean branch name (in netlify.toml), and the branch is available via the HEAD environment variable this could be as simple as adding HEAD to the condition here

netlify-plugin-secrets-manager/src/main.js

Line 99 in 2d09ef8

if (CONTEXT === context) {