add config options for mail encryption and authentication

[wkloucek]

Description

Enhancement: Add configuration options for mail authentication and encryption

We've added configuration options to configure the authentication and encryption
for sending mails in the notifications service.

Furthermore there is now a distinguished configuration option for the username to use
for authentication against the mail server. This allows you to customize the sender address
to your liking. For example sender addresses like my oCIS instance <ocis@owncloud.test> are now possible, too.

Related Issue

• Could not send agains servers using STARTTLS / TLS with authentication

Motivation and Context

How Has This Been Tested?

• tested agains a production mail server

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[ownclouders]

💥 Acceptance test localApiTests-apiArchiver-ocis failed. Further test are cancelled...

[fschade]

LGTM

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
1 Vulnerability
0 Security Hotspots
0 Code Smells

0.0% Coverage
0.0% Duplication