Generate lockfile for using twine

[cognifloyd]

Background

This is another part of introducing pants, as discussed in various TSC meetings.

Related PRs can be found in:

• pantsbuild milestone (which includes PRs since Initialize pantsbuild #5713)
• pantsbuild label (which also includes preparatory PRs that came before adding pantsbuild)

Overview of this PR

This configures pants and generates a lockfile so it can use twine when running the publish goal to publish wheels to pypi.

We will still need more config before we can use pants to just build wheels, let alone publish them. But, this is the last lockfile I know of that we need. Getting this in now reduces the diff with my PoC branch so it is easier to plan the next PRs.

Here is the pants.toml config this PR adds:

st2/pants.toml

Lines 150 to 152 in 2eb18db

	[twine]
	lockfile = "lockfiles/twine.lock"
	version = "twine>=3.7.1,<3.8"

twine version

I copied the pants' default version for twine: https://www.pantsbuild.org/v2.14/docs/reference-twine#version

lockfiles/twine.lock

This lockfile differs from the one that comes with pants because we have different python interpreter constraints.

[amanda11]

LGTM