Freeform object support, safe string operations, URL encoding fixes for C-libcurl

[harlequin-tech]

• Implements freeform object support as the json string of the object. Callers manually decode the json to extract the data. (See #5735).
• Replaces strcpy and strcat with bounded strncpy and strncat for safety.
• Fixes URL encoding for query parameters so the keys and values can contain special characters.
• Tested with 327 endpoint model, subset used for query parameter test and free-form objects.

@zhemant @ityuhui @michelealbano updates on behalf of https://moxion.io.

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[ityuhui]

Thank you for your contribution !

Can you resove the merge confict first ?

[ityuhui]

Hi @harlequin-tech

How is it going ? If the comments are too time consuming to address, can you submit the first part of this PR (freeform object support) in a seperate PR first ? I think it's OK to merge.