Increase limit of payload codecs to 64 KB

[johanstokking]

Summary

Increase the limit of payload codecs to 64 KB.

Follow up on #4312.

Current Situation

The current limit is 40 KB: https://github.com/TheThingsNetwork/lorawan-stack/blob/v3.34/api/ttn/lorawan/v3/messages.proto#L736-L749.

Why do we need this? Who uses it, and when?

We need to comply with TS013-1.0.0: https://resources.lora-alliance.org/technical-specifications/ts013-1-0-0-payload-codec-api.

Proposed Implementation

Increase the limits to 65536 bytes.

Contributing

• I can help by doing more research.
• I can help by implementing the feature after the proposal above is approved.
• I can help by testing the feature before it's released.

Validation

• The feature is tested in a staging environment.
• The feature is documented in The Things Stack Documentation

Code of Conduct

• I agree to follow TTN's Community Code of Conduct.