Add Filter functionality to the Feature Flag list view

Note: This feature was iniitally described as part of #322426 that used to include sorting and filtering of the Feature Flag list view

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Problem to solve

Feature flags in GitLab allow users to manage the availability and rollout of features. Organizations can have a very large number of feature flags to manage. Currently, the list view doesn't allow users to filter the list of feature flags in order to find a specific flag they're looking for.

Current State:

Design

Proposal

Add the filter component to the Feature Flag list view.

Design

Filtering should start with free text matches to the feature flag name and description fields.

Future iteration

Further investigation around the different data available should be done in order to implement more sort and filter options, including:

• Environtment
• Feature flag status (active vs inactive)