Fix DR formatters display in Payload Formatters view

[ryaplots]

Summary

References TheThingsNetwork/lorawan-devices#946

Changes

• Display both - downlink encoder and decoder for device repository formatters

Testing

Steps

1. Open Device Payload Formatters Uplink page, there you should see the uplink decoder (what is returned to the formatters/uplink/decoder request)
2. Open Device Payload Formatters Downlink page, there you should see either only the downlink decoder, or only the downlink encoder or both depending on what is returned in the request for /formatters/downlink/decoder and /formatters/downlink/encoder

Results

Notes for Reviewers

We used to merge all formatters into one on the frontend and then display that for both uplink and downlink. I've changed that to display uplink formatters for the uplink view and downlink formatters in the downlink view. For downlink, there are two formatters, a decoder and an encoder. For device repository formatters we should display both for the user to see.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• Testing: The steps/process to test this feature are clearly explained including testing for regressions.
• Infrastructure: If infrastructural changes (e.g., new RPC, configuration) are needed, a separate issue is created in the infrastructural repositories.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.