[MM-61571]: Add label to form field in channel header (#29553)

* [MA-12]: Add label to form field in channel header

* [MA-12]: Update aria attributes and tests

* [MA-12]: Update snapshots, fix e2e test

* [MA-12]: Fix E2E tests

* [MA-12]: Fix type in test

e2e-tests/cypress/tests/integration/channels/enterprise/system_console/channel_moderation/create_posts_spec.ts

@@ -61,7 +61,7 @@ describe('MM-23102 - Channel Moderation - Create Posts', () => {
 
         // # Check Guest user should not have the permission to create a post on a channel when the option is removed
         // * Guest user should see a message stating that this channel is read-only and the textbox area should be disabled
-        cy.findByTestId('post_textbox_placeholder').should('have.text', 'This channel is read-only. Only members with permission can post here.');
+        cy.findByTestId('post_textbox').should('have.attr', 'placeholder', 'This channel is read-only. Only members with permission can post here.');
         cy.findByTestId('post_textbox').should('be.disabled');
 
         // # As a system admin, check the option to allow Create Posts for Guests and save
@@ -75,7 +75,7 @@ describe('MM-23102 - Channel Moderation - Create Posts', () => {
         // # Check Guest user should have the permission to create a post on a channel when the option is allowed
         // * Guest user should see a message stating that this channel is read-only and the textbox area should be disabled
         cy.findByTestId('post_textbox').clear();
-        cy.findByTestId('post_textbox_placeholder').should('have.text', `Write to ${testChannel.display_name}`);
+        cy.findByTestId('post_textbox').should('have.attr', 'placeholder', `Write to ${testChannel.display_name}`);
         cy.findByTestId('post_textbox').should('not.be.disabled');
     });
 
@@ -92,7 +92,7 @@ describe('MM-23102 - Channel Moderation - Create Posts', () => {
 
         // # Check Member should not have the permission to create a post on a channel when the option is removed.
         // * User should see a message stating that this channel is read-only and the textbox area should be disabled
-        cy.findByTestId('post_textbox_placeholder').should('have.text', 'This channel is read-only. Only members with permission can post here.');
+        cy.findByTestId('post_textbox').should('have.attr', 'placeholder', 'This channel is read-only. Only members with permission can post here.');
         cy.findByTestId('post_textbox').should('be.disabled');
 
         // # As a system admin, check the option to allow Create Posts for Members and save
@@ -106,7 +106,7 @@ describe('MM-23102 - Channel Moderation - Create Posts', () => {
         // # Check Member should have the permission to create a post on a channel when the option is allowed
         // * Member user should see a message stating that this channel is read-only and the textbox area should be disabled
         cy.findByTestId('post_textbox').clear();
-        cy.findByTestId('post_textbox_placeholder').should('have.text', `Write to ${testChannel.display_name}`);
+        cy.findByTestId('post_textbox').should('have.attr', 'placeholder', `Write to ${testChannel.display_name}`);
         cy.findByTestId('post_textbox').should('not.be.disabled');
     });
 });