Add current env name to monitoring store

What does this MR do?

1. Move currentEnvironmentName Vue prop to Vuex store.
2. Added a new setInitialState mutation. In the past, setEndpoints was called in the dashboard onCreated hook to set all endpoints. This is now replaced with setInitialState as currentEnvironmentName (non-endpoint) will be required in the Vuex store. Hence, chose a more generic name.

Why is environment name required in Vuex store?

Annotations fetch routine would require the current dashboard path and current environment name. For that reason, current env name is required in the store so it is accessible for the actions.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team