fix: Allow title override in page attributes

[qhanam]

For every page view, the web client updates the title attribute with the value in window.document.title. This means that the title attribute still cannot be overridden (i.e., #430 did not actually solve #493).

This change allows the title attribute to be overridden when recordPageView is used.

Before

document.title = "sensitive";
pageManager.recordPageView({
            pageId: '/home',
            pageAttributes: {
                title: 'override'
            }
        });
// attributes: { pageId: '/home', title: 'sensitive' }

After

document.title = "sensitive";
pageManager.recordPageView({
            pageId: '/home',
            pageAttributes: {
                title: 'override'
            }
        });
// attributes: { pageId: '/home', title: 'override' }

Discussion

Options for fixing this include the following.

1. Stop recording the page title.
2. Record title at the start of the session only.
3. Session attributes cannot be overwritten.
4. Allow page attributes to be overwritten.

All of these options have problems.

• Regarding (1), we stop giving users a common piece of information.
• Regarding (2), if the title changes during route changes, the new title will not be recorded.
• Regarding (3), this would create special classes of attributes.
• Regarding (4), requires the application to explicitly recording page views, and overwrite the title for each page view.

I am recommending option (4), because it has the least risk with respect to backwards compatibility.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[williazz]

Question: can the override logic be implemented by swapping these two lines instead? https://github.com/aws-observability/aws-rum-web/pull/508/files#diff-93123c2ab6bd111166aa9a50cf26e70a2ee8db05649d6f23e8a4c819a6c3a56fR208-R209

[qhanam]

can the override logic be implemented by swapping these two lines instead?

The only other attributes that could be overridden are pageId and pageTags. These are passed as arguments to recordPageView along with the custom attributes, and so in the original spec we decided that the arguments would take precedence over the attributes.