Extend DORA4 API support for environment name

Release notes

As a user with multiple production environments, I want to be able to see the metric(s) for a specific environment and not necessarily the entire group of production environments. In this issue we are adding the ability to specify a specific environment to retrieve metrics from.

Problem to solve

Coming from #296849 (comment 546261345)

As a user with multiple production environments, I want to be able to see the metric(s) for a specific environment and not necessarily the entire group of production environments.

Proposal

Add environment_name as an optional attribute to the get DORA4 API.

Get project-level DORA metrics.

GET /projects/:id/dora/metrics

Attribute	Type	Required	Description
environment_tier	string	no	The tier of the environment. Default is production.
environment_name	string	no	The name of the environment. Default is production.

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