MM-28014 Improve Channel Intros (#26413)

* added SVGs for channel intros and initial changes to styles and layout

* cleaned up svgs, made theme use theme colors

* updated action buttons in channel intro

* adding mobile view changes

* fixed lint issues

* fixed test issues

* fixed test and i18n issues

* updates to action button styles and reworked grouping of buttons

* updated off-topic and town square intro to remove the add members button

* updated default add members text and groups text

* fixed lint issue on action button css

* imported action button in module scss instead

* fixes from code review

* changed avatar tokens not to be so custom

* fixed type issue with avatar component

* fixed single quote issue with tests

* Revert "changed avatar tokens not to be so custom"

This reverts commit 700f172f0d537b5454d85c5fad5e9aa3f76c26b3.

* Revert "fixed type issue with avatar component"

This reverts commit 5ad1092ba49a10c11ab78247aa5c231e24ed722a.

* fixed avatar types and order of sizes

e2e-tests/cypress/tests/integration/channels/keyboard_shortcuts/keyboard_shortcuts_1_spec.js

@@ -59,13 +59,13 @@ describe('Keyboard Shortcuts', () => {
             });
 
             // # Verify that we are in the test channel
-            cy.get('#channelIntro').contains('.channel-intro__title', `Beginning of ${testChannel.display_name}`).should('be.visible');
+            cy.get('#channelIntro').contains('.channel-intro__title', `${testChannel.display_name}`).should('be.visible');
 
             // # Verify that the right channel is displayed in LHS
             cy.uiGetLhsSection('CHANNELS').findByText(testChannel.display_name).should('be.visible');
 
             // # Verify that the current user(sysadmin) created the channel
-            cy.get('#channelIntro').contains('.channel-intro__content', `This is the start of the ${testChannel.display_name} channel, created by sysadmin`).should('be.visible');
+            cy.get('#channelIntro').contains('.channel-intro__created', 'Public channel created by sysadmin').should('be.visible');
         });
     });