Add TCP Middlewares support

[rtribotte]

What does this PR do?

This PR introduces TCP middleware support:

• Adds TCP Middlewares mechanism
• Adds IPWhitelist as the first TCP middleware (allowing to check the remote address against a source range)
• Updates the API to serve TCP middlewares info
• Updates the WebUI to display TCP middlewares

Motivation

Introduction of the TCP middlewares and fixes #6684

More

• Added/updated tests
• Added/updated documentation

Additionnal notes

Remaining TODOs:

• Write the overview introduction for TCP Middlewares in documentation

[tnelson-doghouse]

rtribotte: I note that there's an unticked task called "Write the overview introduction for TCP Middlewares in documentation", but that there's a commit called "doc: add TCP middlewares overview and IpWhitelist middleware". Does that mean that you did it, but forgot to tick the task? I ask because this PR is listed as having 2/3 complete tasks.

[rtribotte]

Hi @tnelson-doghouse,

Indeed, this task remains unchecked because the introduction page for TCP middleware in the documentation (docs/content/middlewares/tcp/overview.md) needs a proper introduction, and perhaps an illustration too.

[electrical]

I'm curious as what is holding this back from being merged? This functionality and the original use case is exactly what i'm looking for :-)
Thanks.

[rtribotte]

Hello @electrical,

Thanks for your interest in Traefik!

This PR is labeled as needs-design-review, as you can see in our contribution guide, this means that we have to take a closer look at the scope of impact for that PR to see, how it would interact with the other parts of Traefik.

[Secursus]

HI,

I'm looking forward to this PR...

it is still up to date ?

[cma1kep]

Hello,

any changes in Review?

[dtomcej]

LGTM

[ldez]

LGTM