Accept --no-echo to turn off run.echo

[zed]

It may be useful to override run.echo parameter if it is set already in a config file/environment variable.

Consider tasks.py:

from invoke import task

@task
def print_echo_param(c):
    c.run(f"echo '{c.config.run.echo=}'")

Then:

$ inv print-echo-param
c.config.run.echo=False

$ inv --echo print-echo-param
echo 'c.config.run.echo=True'
c.config.run.echo=True

If there is export INVOKE_RUN_ECHO=1 then:

$ inv print-echo-param
echo 'c.config.run.echo=True'
c.config.run.echo=True

$ INVOKE_RUN_ECHO=0 inv print-echo-param
c.config.run.echo=False

It would be nice to provide --no-echo instead of INVOKE_RUN_ECHO=0 here.

The current version doesn't recognize --no-echo parameter:

inv --no-echo print-echo-param
No idea what '--no-echo' is!