Escape dashboard paths

What does this MR do?

Fixes #206945 (closed)

Dashboard paths need to be encoded in the cases where they are used as query parameters. Otherwise they can cause issues when parsing parameters.

For example in the case of .../metrics?dashboard=.gitlab/dashboards/common_metrics%26copy.yml the percent encoded & (%26) is interpreted as a separate query param. As seen in https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/lib/utils/url_utility.js#L52-63, we first decode the params and then split via &. To fix this we need to double encode the dashboard path.

This MR does three things:

1. URL encodes the dashboard path when selecting a dashboard via the dropdown and sending the request to the backend.
2. URL decodes the dashboard path when setting it in the store on the frontend.
3. URL decodes the dashboard path on the backend.

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