*) mod_md: update to version 2.6.1

  *) mod_md: update to version 2.6.1
     - Increasing default `MDRetryDelay` to 30 seconds to generate less bursty
       traffic on errored renewals for the ACME CA. This leads to error retries
        of 30s, 1 minute, 2, 4, etc. up to daily attempts.
     - Checking that configuring `MDRetryDelay` will result in a positive
       duration. A delay of 0 is not accepted.
     - Fix a bug in checking Content-Type of responses from the ACME server.
     - Added ACME ARI support (rfc9773) to the module. Enabled by default. New
       directive "MDRenewViaARI on|off" for controlling this.
     - Removing tailscale support. It has not been working for a long time
       as the company decided to change their APIs. Away with the dead code,
       documentation and tests.
     - Fixed a compilation issue with pre-industrial versions of libcurl.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1927807 13f79535-47bb-0310-9956-ffa450edef68