Add ubus-tmate to expose tmate control for terminal sharing

[nicopace]

This PR proposes an interface to a package that allows console sessions to be shared amongst many people.

This is a piece of a feature that will allow, through the lime-app, for users to request support to other networks and be able to monitor what they do with the access it was given, and remove the access once the intervention is done or you don't want them to be accessing your router anymore. It will have as a lime-app screen.

https://user-images.githubusercontent.com/1136597/104211357-bd7a8580-5412-11eb-9d9b-74123590c28e.mp4
(Chrome plays it, Firefox doesn't :( )

Opening it up so to get your general feedback on:

• using tmate instead of lime-remotesupport: I think it is good that we can generalize it, we will eventually be able to upstream it

You will have to add the tmate feed to your OpenWRT buildroot to build it src-git tmate https://github.com/project-openwrt/openwrt-tmate.git. It needs OpenWRT 19.07.0 as it needs libssh 0.7.6.

[codecov-io]

Codecov Report

Merging #839 (0e54867) into master (0dbbc8a) will increase coverage by 0.21%.
The diff coverage is 91.42%.

@@            Coverage Diff             @@
##           master     #839      +/-   ##
==========================================
+ Coverage   72.19%   72.40%   +0.21%     
==========================================
  Files          38       39       +1     
  Lines        3334     3378      +44     
==========================================
+ Hits         2407     2446      +39     
- Misses        927      932       +5     

Impacted Files	Coverage Δ
packages/ubus-tmate/files/usr/lib/lua/tmate.lua	88.63% <91.42%> (ø)

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[germanferrero]

Looks great @nicopace. I'll test it out with final version of the limeapp and report back

[nicopace]

How do we do with this package that requires a package from a different feed?
Should we add something in the readme to instruct which feeds need to go with this one?

[spiccinini]

Great PR! Good work Nico!

This is just a "administrative" request (and a reminder for everyone included myself), plase can you modify your commit mesages so they start with the module name that is modified? (like ubus-tmate: fix bla bla) this greatly simplifies going through the commit logs. And while you are at it some cosmetics: please remove the final dot and use 'fix bla bla' instead of 'fixes bla bla'. Yes, we should add this recomendations in the contributing info.
A quick way to do it is to do: git rebase -i master and then replace all the pick by reword (save and close) and then all the commit mesages will be desplayed for you to be changed.

[germanferrero]

I've test it against libremesh/lime-app#289 and works great