feat(common.opcua): Add string configuration option for node ID

[skartikey]

Summary

Adds support for specifying OPC UA node IDs using the standard string format (e.g., ns=0;i=2262 or nsu=http://...;s=Name) as an alternative to specifying namespace, identifier_type, and identifier separately.

• Users can now configure nodes using the simpler node_id string that matches what OPC UA browsers display
• The existing configuration style using individual fields (namespace, identifier_type, identifier) continues to work unchanged
• Both styles can be used in the same configuration file (but not for the same node)

New style (recommended for simplicity):

  [[inputs.opcua.nodes]]                                                                                                                                                                                                           
    name = "ProductUri"                                                                                                                                                                                                            
    id = "ns=0;i=2262"    

Existing style (still fully supported):

  [[inputs.opcua.nodes]]                                                                                                                                                                                                           
    name = "ProductUri"                                                                                                                                                                                                            
    namespace = "0"                                                                                                                                                                                                                
    identifier_type = "i"                                                                                                                                                                                                          
    identifier = "2262"   

Supported node ID formats:

• Namespace index: ns=0;i=2262, ns=2;s=Device.Temp
• Namespace URI: nsu=http://opcfoundation.org/UA/;i=2255
• All identifier types: i (numeric), s (string), g (GUID), b (opaque)

Checklist

• No AI generated code was used in this PR
• AI generated code used in this PR follows the InfluxData Policy on AI-Generated Code Contributions

Related issues

resolves #12396

[srebhan]

Thanks @skartikey! Some comments from my side.

[srebhan]

Awesome job @skartikey!

[mstrandboge]

Overall looks great! I just have one tiny comment

[telegraf-tiger]

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Artifact URLs

. DEB	. RPM	. TAR . GZ	. ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz