use debug- prefix for Yamux experimental support

[tersec]

Discussed in #5080 (comment)

per https://nimbus.guide/options.html#available-options

Any debug-prefixed flags are considered ephemeral and subject to removal without notice.

It's already not documented because it's hidden; this just makes the existing policy explicit.

[github-actions]

Unit Test Results

         9 files  ±0    1 107 suites  ±0   23m 6s ⏱️ - 1m 52s
  4 233 tests ±0    3 886 ✔️ ±0  347 💤 ±0  0 ❌ ±0 
16 894 runs  ±0  16 496 ✔️ ±0  398 💤 ±0  0 ❌ ±0 

Results for commit 2779d2c. ± Comparison against base commit 0d48535.

[zah]

Looks like the old name is in use here:
https://github.com/status-im/infra-nimbus/blob/aaa3c437a9bc23e5be854940990ce10d91f2bef9/ansible/group_vars/nimbus.mainnet.yml#L171

@jakubgs, would you coordinate this change?

[jakubgs]

Should I make the change before this is merged?

[tersec]

Should I make the change before this is merged?

If it's only the libp2p nodes without any validators (because mainnet test fleet) anyway, yeah. Make the change there, I'll merge, and within 24 hours, things will be synced again.