Reimplement tls-alpn-01 in acme (#6886)

This PR is the first part of work described in #6724.

It reintroduces the tls-alpn-01 challenge in `acme` module, that was introduced by #5894 and reverted by #6100. The reason it was removed in the past is because some tests showed that with `1.0.2` branch of OpenSSL, the self-signed certificate containing the authorization key is sent to the requester even if the ALPN protocol `acme-tls/1` was not declared as supported by the requester during the TLS handshake.

However recent discussions lead to the conclusion that this behavior was not a security issue, because first it is coherent with the behavior with servers that do not support ALPN at all, and second it cannot make a tls-alpn-01 challenge be validated in this kind of corner case.

On top of the original modifications given by #5894, I merged the code to be up-to-date with our `master`, and fixed tests to match recent evolution about not displaying the `keyAuthorization` in the deserialized JSON form of an ACME challenge.

I also move the logic to verify if ALPN is available on the current system, and so that the tls-alpn-01 challenge can be used, to a dedicated static function `is_available` in `acme.challenge.TLSALPN01`. This function is used in the related tests to skip them, and will be used in the future from Certbot plugins to trigger or not the logic related to tls-alpn-01, depending on the OpenSSL version available to Python.

* Reimplement TLS-ALPN-01 challenge and standalone TLS-ALPN server from #5894.

* Setup a class method to check if tls-alpn-01 is supported.

* Add potential missing parameter in validation for tls-alpn

* Improve comments

* Make a class private

* Handle old versions of openssl that do not terminate the handshake when they should do.

* Add changelog

* Explicitly close the TLS connection by the book.

* Remove unused exception

* Fix lint

1 files changed, 13 insertions, 0 deletions

diff --git a/acme/tests/testdata/rsa1024_cert.pem b/acme/tests/testdata/rsa1024_cert.pem
new file mode 100644
index 000000000..1b7912181
--- /dev/null
+++ b/acme/tests/testdata/rsa1024_cert.pem
@@ -0,0 +1,13 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----