Add environment name search that returns environment id

What does this MR do?

This closes #37969 (closed). We need an endpoint that allows for the searching of environments by name and returns both id and name. We have an existing endpoint Projects::EnvironmentsController#search that only returns the names of the environments, and changing that to include the ids as well would break the implementation for the current consumer of that endpoint. Therefore, a very similar endpoint has been added Projects::EnvironmentsController#search_for_id that searches a project's environments for a matching name and returns both the name and the id.

This environment search https://docs.gitlab.com/ee/api/environments.html#list-environments will not work for this purpose because we need the search to work on partial matches as the user is typing.

tagging @dbodicherla

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Does this MR meet the acceptance criteria?

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• Changelog entry
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