Deprecate config for timeout_commit and timeout_propose

[rootulp]

Context

celestiaorg/celestia-app#3882 made the config timeout_commit and timeout_propose unused in app version >= 3.

Motivation

celestiaorg/celestia-app#4080 (comment)

Problem

On main, if I run celestia-appd init then I see a config.toml like this:

# How long we wait for a proposal block before prevoting nil
timeout_propose = "3.5s"

# How long we wait after committing a block, before starting on the new
# height (this gives us a chance to receive some more precommits, even
# though we already have +2/3).
timeout_commit = "4.2s"

The config doesn't mention that these two fields are deprecated in v3.x and have no effect.

Proposal

Add a comment that says these fields are deprecated for app version >= 3.