URL params in monitoring sets existing variables

Background

Currently, URL params in the monitoring dashboard are extracted and rendered as text inputs. The values of these text inputs are eventually passed to the Prometheus API.

However, only templating variables defined in the dashboard yml file should be rendered as dropdown/text inputs in the monitoring dashboard (this is the issue #214533 (closed)). As for URL params, they should update the values of these inputs and not render new ones.

What does this MR do?

1. Prevents the URL params from rendering new text inputs.
2. Updates the URL param extraction logic to update the promVariables store property only for existing keys.

Note

promVariables store property will be empty. The logic to parse out variables from yml file and render inputs is WIP !31524 (merged).

Once !31524 (merged) goes in, promVariables will have the list of all the variables that need to be rendered. After that this MR would complement the feature to update only existing variables.

Screenshots

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