Add optional 'EmailFrom' configuration to NGAS Utils

[szampier]

This backward-compatible change affects only the NGAS utilities (likely used only at ESO). It introduces a new optional parameter in the ~/.ngas configuration file to address an issue with email notifications sent by the xsync tool.

Summary by Sourcery

Enhancements:

• Introduce an optional EmailFrom parameter in the NGAS configuration to override the default sender address for notification emails.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adds an optional EmailFrom configuration parameter for NGAS utilities and updates xsync email sending logic to use it while preserving the existing default behavior.

Sequence diagram for updated send_email EmailFrom resolution

sequenceDiagram
    actor User
    participant Xsync
    participant NgasUtilsLib
    participant NgasResourceFile
    participant SmtpServer

    User->>Xsync: Trigger xsync operation
    Xsync->>NgasUtilsLib: send_email(subject, to, message)
    NgasUtilsLib->>NgasResourceFile: get_parameter_ngas_resource_file(SmtpHost)
    NgasResourceFile-->>NgasUtilsLib: smtp_host or empty
    alt smtp_host is empty
        NgasUtilsLib-->>Xsync: Print error No SMTP host defined in RC file
    else smtp_host is defined
        NgasUtilsLib->>NgasResourceFile: get_parameter_ngas_resource_file(EmailFrom)
        NgasResourceFile-->>NgasUtilsLib: email_from or empty
        alt EmailFrom is defined
            NgasUtilsLib->>NgasUtilsLib: from_field = email_from
        else EmailFrom is not defined
            NgasUtilsLib->>NgasUtilsLib: from_field = getpass_user@host
        end
        NgasUtilsLib->>SmtpServer: Connect and send email with from_field
        SmtpServer-->>User: Deliver notification email
    end

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Flow diagram for send_email with optional EmailFrom override

flowchart TD
    A[send_email called] --> B[Read SmtpHost from NGAS RC file]
    B --> C{SmtpHost defined?}
    C -- No --> D[Print error No SMTP host defined in RC file]
    D --> E[Return]
    C -- Yes --> F[Read EmailFrom from NGAS RC file]
    F --> G{EmailFrom defined?}
    G -- Yes --> H[Set from_field = EmailFrom]
    G -- No --> I[Set from_field = getpass_user@host]
    H --> J[Split recipient list and send via SMTP]
    I --> J[Split recipient list and send via SMTP]
    J --> K[End]

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File-Level Changes

Change	Details	Files
Introduce configurable email sender address with backward-compatible fallback.	Add new NGAS_RC_PAR_EMAIL_FROM constant for the EmailFrom configuration key in the NGAS resource file. Update send_email() to read the EmailFrom value from the NGAS configuration via get_parameter_ngas_resource_file. Fallback to the previous from_field value based on the current user and host when EmailFrom is not configured. Keep the rest of the email sending logic (SMTP resolution, recipient parsing, headers) unchanged.	src/ngamsUtils/ngamsUtils/ngasUtilsLib.py

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[sourcery-ai]

Hey - I've left some high level feedback:

• When reading NGAS_RC_PAR_EMAIL_FROM, consider normalizing the value (e.g., strip() and verifying it is non-empty and looks like an email address) before using it, so that misconfigured or whitespace-only values don’t silently fall back or produce an invalid From header.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- When reading `NGAS_RC_PAR_EMAIL_FROM`, consider normalizing the value (e.g., `strip()` and verifying it is non-empty and looks like an email address) before using it, so that misconfigured or whitespace-only values don’t silently fall back or produce an invalid `From` header.

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