Add script to configure partner NTP server in chrony

[Copilot]

Implements automated update of /etc/rdk_chrony.conf with partner NTP server URL in chrony format.

Implementation

• Script: update-chrony-config.sh reads partner URL from /etc/partner_url.conf or PARTNER_NTP_URL env var, validates input, writes chrony server directive
• Recipe: chrony-config.bb installs script to /usr/sbin/ and config template to /etc/
• Format: Generates server <url> iburst minpoll 10 maxpoll 12 per chrony spec

Security

Input validation prevents injection attacks:

• POSIX-compliant newline detection via case pattern matching
• Hostname/IP format validation (no consecutive dots, proper structure)
• Port range enforcement (1-65535)
• Printf-based output (no interpolation risks)

Usage

# Via config file
echo "PARTNER_NTP_URL=ntp.partner.example.com" > /etc/partner_url.conf
/usr/sbin/update-chrony-config.sh

# Via environment variable  
PARTNER_NTP_URL=ntp.partner.example.com /usr/sbin/update-chrony-config.sh

Add chrony-config to image recipe to include in build.

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