Remove asChipUnderlyingType helper

[vivien-apple]

Problem

In many places into our templates {{asUnderlyingZclType type}} is used to retrieve which types should be used for the signature of methods. But it does not return the proper type for octet_string nor long_octet_string at the moment so there in many places the code has been written such as:

{{#if (isOctetString type)}}chip::ByteSpan{{else}}{{asUnderlyingZclType type}}{{/if}}

This PR adds octet_string and long_octet_string to override.js so the code can be rewritten such as:

{{asUnderlyingZclType type}}

And in a few other places, the code assume that octet_string means the chip::ByteSpan class which is not very convenient if at some point this type needs to be updated...

Change overview

• Return the expected type into override.js
• Clean up the places where {{#if (isOctetString type)}} is useless now

Testing

The only code changes that is generated is ATTRIBUTE_ID -> ATTRIB_ID into a comment. So nothing has really changed.

[bzbarsky-apple]

So nice to see all that conditional junk go away!