docs: fixed typo

Fixed typo: programatic/programmatic

nomad exec part 3: executor based drivers

These simply delegate call to backend executor.

Implements streamign exec handling in both executors (i.e. universal and
libcontainer).

For creation of TTY, some incidental complexity leaked in.  The universal
executor uses github.com/kr/pty for creation of TTYs.

On the other hand, libcontainer expects a console socket and for libcontainer to
create the underlying console object on process start.  The caller can then use
`libcontainer.utils.RecvFd()` to get tty master end.

I chose github.com/kr/pty for managing TTYs here.  I tried
`github.com/containerd/console` package (which is already imported), but the
package did not work as expected on macOS.

Prepare executor to handle streaming exec API calls that reuse drivers protobuf
structs.

UI: Fixed flaky client-detail test

Added Sparrow link

Setup probot/stale

* Added info about scheduler fail and success cases

* fix "and and"; copypasta

* Moving links to bottom for consistency

* Adopted @schmichael wording

Fix website links

https://github.com/hashicorp/nomad/pull/5667 restructured lots of
guides; this adds redirects to ensure that old links work.

doc: wording

Fixed wording: "as show below" -> "as shown below".

nomad exec part 1: plumbing and docker driver

Adds nomad exec support in our API, by hitting the websocket endpoint.

We introduce API structs that correspond to the drivers streaming exec structs.

For creating the websocket connection, we reuse the transport setting from api
http client.

Add consolidated testing package to serve as conformance tests for all drivers.

This adds a websocket endpoint for handling `nomad exec`.

The endpoint is a websocket interface, as we require a bi-directional
streaming (to handle both input and output), which is not very appropriate for
plain HTTP 1.0. Using websocket makes implementing the web ui a bit simpler. I
considered using golang http hijack capability to treat http request as a plain
connection, but the web interface would be too complicated potentially.

Furthermore, the API endpoint operates against the raw core nomad exec streaming
datastructures, defined in protobuf, with json serializer.  Our APIs use json
interfaces in general, and protobuf generates json friendly golang structs.
Reusing the structs here simplify interface and reduce conversion overhead.

Add a client streaming RPC endpoint for processing nomad exec tasks, by invoking
the relevant task handler for execution.

Also add a helper that converts the adapts the high level interface to the
low-level interface of nomad exec interfaces.

Revised NomadProject Structure

remove Index field from EmitNodeEventsResponse