Add AuthenSASL to perl deps; improve email docs

Dependencies

• [2] 3JXCTKEC Add markdown files for documentation
• [*] RWNXH3H2 lastModified -> lastModifiedDate

Change contents

• edit in doc/manual/src/projects.md at line 460
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  +

  + The feature can be turned on by adding the following line to `hydra.conf`

  +

  + ``` conf

  + email_notification = 1

  + ```

  +

  + By default, Hydra only sends email notifications if a previously successful

  + build starts to fail. In order to force Hydra to send an email for each build

  + (including e.g. successful or cancelled ones), the environment variable

  + `HYDRA_FORCE_SEND_MAIL` can be declared:

  +

  + ``` nix

  + services.hydra-dev.extraEnv.HYDRA_FORCE_SEND_MAIL = "1";

  + ```
• edit in doc/manual/src/projects.md at line 476
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  + SASL Authentication for the email address that's used to send notifications

  + can be configured like this:

  +

  + ``` conf

  + EMAIL_SENDER_TRANSPORT_sasl_username=hydra@example.org

  + EMAIL_SENDER_TRANSPORT_sasl_password=verysecret

  + EMAIL_SENDER_TRANSPORT_port=587

  + EMAIL_SENDER_TRANSPORT_ssl=starttls

  + ```

  +

  + Further information about these environment variables can be found at the

  + [MetaCPAN documentation of `Email::Sender::Manual::QuickStart`](https://metacpan.org/pod/Email::Sender::Manual::QuickStart#specifying-transport-in-the-environment).

  +

  + It's recommended to not put this in `services.hydra-dev.extraEnv` as this would

  + leak the secrets into the Nix store. Instead, it should be written into an

  + environment file and configured like this:

  +

  + ``` nix

  + { systemd.services.hydra-notify = {

  + serviceConfig.EnvironmentFile = "/etc/secrets/hydra-mail-cfg";

  + };

  + }

  + ```

  +
• edit in flake.nix at line 293
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  + AuthenSASL