Gradually increasing HSTS max-age (#5912)

This PR adds the functionality to enhance Apache configuration to include HTTP Strict Transport Security header with a low initial max-age value.

The max-age value will get increased on every (scheduled) run of certbot renew regardless of the certificate actually getting renewed, if the last increase took place longer than ten hours ago. The increase steps are visible in constants.AUTOHSTS_STEPS.

Upon the first actual renewal after reaching the maximum increase step, the max-age value will be made "permanent" and will get value of one year.

To achieve accurate VirtualHost discovery on subsequent runs, a comment with unique id string will be added to each enhanced VirtualHost.

* AutoHSTS code rebased on master

* Fixes to match the changes in master

* Make linter happy with metaclass registration

* Address small review comments

* Use new enhancement interfaces

* New style enhancement changes

* Do not allow --hsts and --auto-hsts simultaneuously

* MyPy annotation fixes and added test

* Change oldest requrements to point to local certbot core version

* Enable new style enhancements for run and install verbs

* Test refactor

* New test class for main.install tests

* Move a test to a correct test class

certbot-apache/setup.py

@@ -8,7 +8,7 @@ version = '0.26.0.dev0'
 # acme/certbot version.
 install_requires = [
     'acme>0.24.0',
-    'certbot>=0.21.1',
+    'certbot>0.25.1',
     'mock',
     'python-augeas',
     'setuptools',