Expose TERM and COLORTERM (and maybe other) system env vars to ddev

[hanoii]

I am doing this on an add on: https://github.com/hanoii/ddev-pimp-my-shell/blob/1c5d2f5cd667edd7236c97844b172e769f0f67d3/config.pimp-my-shell.yaml#L25-L26, specially TERM was one that was bugging me as I use https://sw.kovidgoyal.net/kitty/faq/ that has needs its own termcap to function properly.

I wonder why this is not something happening by default, exposing useful and personal system environment variables to the running ddev if whether it should.

[rfay]

We go to a lot of effort to do COLUMNS and such. Last time I was in this territory there was too much friction between the shell in container and the shell on host to make it work, but contribution is welcome there.