Add documentation for profile selectors (#4120)

Ref #4018

docs/docs/how-to/profile_selectors.md

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+---
+sidebar_position: 130
+title: Apply a profile to a subset of entities
+---
+
+# Apply a profile to a subset of entities
+
+Profiles allow you to apply a consistent set of rules to a group of entities within your project. By default, these
+profiles are applied universally across all entities in a project. However, you may need to target a specific subset, such as
+repositories belonging to a specific organization. Minder simplifies this process with profile selectors, enabling you
+to easily customize which entities a profile applies to.
+
+## Prerequisites
+
+- The `minder` CLI application
+- A Minder account with
+  [at least `editor` permission](../user_management/user_roles.md)
+- An enrolled Provider (e.g., GitHub) and registered repositories
+
+## Add a selector to a profile
+
+Selectors are written using [CEL (Common Expression Language)](https://github.com/google/cel-spec). To add a selector to
+your profile, you need to define the entity and the condition you want to apply. Below is an example showing how to
+configure a selector to filter repositories and artifacts:
+
+```yaml
+name: profile-with-selectors
+selection:
+  - entity: repository
+    selector: repository.is_fork != true && repository.name.startsWith('stacklok/')
+  - entity: artifact
+    selector: artifact.provider.name == 'github-app-stacklok'
+```
+
+Let's break down the example above:
+- `entity`: Defines the type of entity you want to filter (`repository`, `artifact`, or `pull_request`). In the case that the `entity` type is omitted, the selector will be applied to all entities.
+- `selector`: The CEL expression that specifies the filtering criteria. In the example:
+  - The first selector filters repositories to include only those that are not forks and whose name starts with stacklok. In other words, those that are part of the stacklok organization.
+  - The second selector filters artifacts to include only those provided by `github-app-stacklok`.
+
+Below you can find the full list of selectors available for each entity type.
+
+## Repository selectors
+
+Selectors for repositories allow you to filter and manage repositories based on specific attributes.
+
+| Field        | Description                                                                                           | Type             |
+|--------------|-------------------------------------------------------------------------------------------------------|------------------|
+| `name`       | The full name of the repository, e.g. stacklok/minder                                                 | string           |
+| `is_fork`    | `true` if the repository is a fork, `nil` if unknown or not applicable to this provider               | bool             |
+| `is_private` | `true` if the repository is private, `nil` if unknown or not applicable to this provider              | bool             |
+| `provider`   | The provider of the repository, for more details see [Provider Selectors](#entity-provider-selectors) | ProviderSelector |
+
+## Artifact selectors
+
+| Field      | Description                                                                                         | Type             |
+|------------|-----------------------------------------------------------------------------------------------------|------------------|
+| `name`     | The full name of the artifact, e.g. stacklok/minder-server                                          | string           |
+| `type`     | The type of the artifact, e.g. "container"                                                          | string           |
+| `provider` | The provider of the artifact, for more details see [Provider Selectors](#entity-provider-selectors) | ProviderSelector |
+
+## Pull request selectors
+
+| Field  | Description                                                 | Type   |
+|--------|-------------------------------------------------------------|--------|
+| `name` | The full name of the pull request, e.g. stacklok/minder/123 | string |
+
+## Entity provider selectors
+
+Each entity can be filtered based on its provider.
+
+| Field   | Description                                        | Type   |
+|---------|----------------------------------------------------|--------|
+| `name`  | The name of the provider, e.g. github-app-stacklok | string |
+| `class` | The class of the provider, e.g. github-app         | string |