add pty_no_echo option

[blueyed]

Ref: #9107

Given the number of options there are already, channel_job_start should be passed a struct for those instead maybe?

Also this uses pty_no_echo mainly because tv_dict_get_number defaults to 0 for a non-existing entry - but it is also clearer.

However, also for jobstart() it might make sense to at least group termios settings?!

[bfredl]

should be a sub-dict to jobstart() options. If we add this option, it is reasonable to expect more flags will be requested.

we should probably make all pty related state a struct to common_job_start() (including size and TERM), to make the signature more manageable.

[justinmk]

However, also for jobstart() it might make sense to at least group termios settings?!

See also #6992, there were tentative plans to make all termios options user-settable via jobstart().

Sub-dict is unfortunate but I don't have a better idea (string flags?).