…pec installs

Closes: denoland#20744

Adds ability to specify the kernelspec location for deno kernel with
--directory flag

Continued default behavior installs in user's kernelspec folder via
jupyter shelling out:
`deno jupyter --install`

Advanced installs can specify their own path:
`deno jupyter --install --directory ~/.kernelspec_custom_location/deno`

In the advanced case deno builds and installs the files directly rather
than relying on calling out to jupyter to determine path.

This is useful in the circumstance where jupyter is not on PATH at time
of installing deno jupyter, but it is available and used via a wrapping
library.

This reverts commit 5286f0a.

Co-authored-by: Bartek Iwańczuk <[email protected]>
Signed-off-by: Zander Hill <[email protected]>