cli: debug sub-command (#4227)

## Issue

Implement a new subcommand: tendermint debug. This subcommand itself has two subcommands:

    $ tendermint debug kill <pid> </path/to/out.zip> --home=</path/to/app.d>

Writes debug info into a compressed archive. The archive will contain the following:

├── config.toml
├── consensus_state.json
├── net_info.json
├── stacktrace.out
├── status.json
└── wal

The Tendermint process will be killed.

    $ tendermint debug dump </path/to/out> --home=</path/to/app.d>

This command will perform similar to kill except it only polls the node and dumps debugging data every frequency seconds to a compressed archive under a given destination directory. Each archive will contain:

├── consensus_state.json
├── goroutine.out
├── heap.out
├── net_info.json
├── status.json
└── wal

Note:

    goroutine.out and heap.out will only be written if a profile address is provided and is operational.
    This command is blocking and will log any error.

replaces: #3327
closes: #3249

## Commits:

* Implement debug tool command stubs

* Implement net getters and zip logic

* Update zip dir API and add home flag

* Add simple godocs for kill aux functions

* Move IO util to new file and implement copy WAL func

* Implement copy config function

* Implement killProc

* Remove debug fmt

* Validate output file input

* Direct STDERR to file

* Godoc updates

* Sleep prior to killing tail proc

* Minor cleanup of godocs

* Move debug command and add make target

* Rename command handler function

* Add example to command long descr

* Move current implementation to cmd/tendermint/commands/debug

* Update kill cmd long description

* Implement dump command

* Add pending log entry

* Add gosec nolint

* Add error check for Mkdir

* Add os.IsNotExist(err)

* Add to debugging section in running-in-prod doc

docs/tendermint-core/running-in-production.md

@@ -141,6 +141,19 @@ returns just the votes seen at the current height.
 - [StackOverflow
   questions](https://stackoverflow.com/questions/tagged/tendermint)
 
+### Debug Utility
+
+Tendermint also ships with a `debug` sub-command that allows you to kill a live
+Tendermint process while collecting useful information in a compressed archive
+such as the configuration used, consensus state, network state, the node' status,
+the WAL, and even the stacktrace of the process before exit. These files can be
+useful to examine when debugging a faulty Tendermint process.
+
+In addition, the `debug` sub-command also allows you to dump debugging data into
+compressed archives at a regular interval. These archives contain the goroutine
+and heap profiles in addition to the consensus state, network info, node status,
+and even the WAL.
+
 ## Monitoring Tendermint
 
 Each Tendermint instance has a standard `/health` RPC endpoint, which