Add DAST profiles components README

ee/app/assets/javascripts/security_configuration/dast_profiles/README.md

+# DAST profiles components
+
+This document's purpose is to give a broad overview of how DAST profiles apps are structured.
+This summary is deliberately abstract so that it doesn't require frequent updates whenever features are
+added, changed, or removed in DAST profiles.
+
+## DAST profiles list
+
+The DAST profiles list relies on 4 main components that orchestrate the rendering of both profile
+types.
+
+- `DastProfiles` is the top-level component. It acts as the data layer by communicating with the
+  GraphQL API and rewriting the cache as needed. It renders the profile-specific components and
+  ensures they receive the updated data through props and events.
+- `DastSiteProfilesList` and `DastScannerProfilesList` are the profile-specific components. They
+  can implement some logic specific to a profile type if needed. Their rendering is delegated to
+  a shared `DastProfilesList` component that can be extended through slots.
+- `DastProfilesList` is responsible for actually rendering a profiles list. As stated above, it
+  is rendered by a profile-specific component that provides profiles data and optionally customizes
+  what's displayed using slots.
+
+```mermaid
+graph TD;
+  subgraph Profile list;
+  DP(dast_profiles.vue)
+  SCPL[dast_scanner_profiles_list.vue]
+  SIPL[dast_site_profiles_list.vue]
+  DPL[dast_profiles_list.vue]
+  DP -- render --> SCPL
+  DP -- render --> SIPL
+  SCPL -- render --> DPL
+  SIPL -- render --> DPL
+  end;
+```
+
+## DAST profiles forms
+
+To render DAST profile forms, we have 3 components and a mixin.
+A base component implements all the logic that can be shared across both profile types, including: form
+submission, saving a profile, rendering the form's control. For the specific data and behaviors, we have two
+profile-specific components
+
+- `BaseDastProfileForm` implements the logic that can be shared across both profile types like form
+  submission, saving a profile, rendering the form's control, etc.
+- `DastSiteProfileForm` and `DastScannerProfileForm` are profile-specific. They hold the form data
+  and they both render the base component mentioned above. Among other things, they pass computed
+  GraphQL options to the base component via props so that the mutations can be triggered properly.
+  The base component's template is extended with the profile-specific form fields.
+- `dastProfileFormMixin` is the mixin that both profile-specific components leverage to share some
+  common options like props, computed props, etc.
+
+```mermaid
+graph TD;
+  subgraph Site and Scanner profile forms;
+  M(dast_profile_form_mixin.js)
+  SC[dast_scanner_profile_form.vue]
+  SI[dast_site_profile_form.vue]
+  B(base_dast_profile_form.vue)
+  M -- included --> SC
+  M -- included --> SI
+  SC -- render --> B
+  SI -- render --> B
+  end;
+```
+
+## DAST profile selectors
+
+Profile selectors can be used to associate DAST site and scanner profiles with an on-demand DAST
+scan, or when configuring DAST for a project. Thus, they have been abstracted out in a reusable
+component that itself relies on a set of reusable components.
+
+- `DastProfilesSelector` is the main component that fetches the profiles and renders the
+  profile-specific selectors.
+- `ScannerProfileSelector` and `SiteProfileSelector` both render two common base components that they
+  extend through props and slots.
+- `ProfileSelector` is the base component responsible for rendering the actual selector.
+- `ScannerProfileSummary` and `SiteProfileSummary` are the base components responsible for rendering selected profiles'
+  summary. It relies on `SummaryCell` to render each data-point in the summary.
+
+```mermaid
+graph TB;
+  S(dast_profiles_selector.vue)
+  ScannerSelector[scanner_profile_selector.vue]
+  SiteSelector[site_profile_selector.vue]
+  PS[profile_selector.vue]
+  ScannerSelectorSummary[scanner_profile_summary.vue]
+  SiteSelectorSummary[site_profile_summary.vue]
+  ProfileSelectorSummaryCell[summary_cell.vue]
+
+  subgraph Selector;
+    direction TB;
+    S --> ScannerSelector
+    S --> SiteSelector
+    ScannerSelector --> PS
+    SiteSelector --> PS
+  end;
+
+  subgraph Profile summary;
+    direction TB;
+    ScannerSelector --> ScannerSelectorSummary
+    ScannerSelectorSummary --> ProfileSelectorSummaryCell
+    SiteSelector -->SiteSelectorSummary
+    SiteSelectorSummary --> ProfileSelectorSummaryCell
+  end;
+```