update_campaign / draft_campaign: set campaign URL options (tracking template, final URL suffix, custom parameters) #105

Situation. We tag all paid traffic with UTM parameters through a campaign-level tracking template, so analytics can attribute sessions and conversions by campaign, ad group and keyword. After building two Search campaigns through AdLoop, the template was one of the few settings that still needed the Google Ads UI. The weekly check also can't confirm it's still set without a hand-written GAQL query.

What I tried. draft_campaign and update_campaign have no URL options. run_gaql reads campaign.tracking_url_template (both new campaigns: empty), but nothing writes it.

What the API offers. Three fields on Campaign:

• tracking_url_template: a string with {lpurl} and ValueTrack parameters
• final_url_suffix
• url_custom_parameters: a list of CustomParameter{key, value}

Proposed change. Optional tracking_url_template, final_url_suffix and url_custom_parameters on draft_campaign and update_campaign, all omitted by default. Validation:

• the template must contain {lpurl} or one of its variants
• custom parameter keys and values are checked against Google's length limits

The preview would show the template applied to the campaign's final URL, so a typo is visible before it's applied. The dry run already catches anything Google rejects.

Happy to PR once you're happy with the shape. It touches the same files as the location option (#104), so the two could share a PR or go one after the other, whichever you prefer.