Document deprecation process

[mariajgrimaldi]

Description

As a result of this PR, which adds a filter to a legacy page, we must decide and document a deprecation strategy. How should we monitor this effort?

@felipemontoya suggests:

• for the page is being removed, I am notified for one stable release
• when possible, the filter is used in the new replacement page or the API that MFEs call for the same feature. Otherwise a different but equivalent filter exists for the replacement page.

A strategy I agree with, For now, we will track each filter to check which ones are candidates for deprecation, so we can track them better.