fix: [Integrations > Add integration prompt][SCREEN READER]: Images a…

…re decorative and should be removed from the accessibility tree (elastic#179805)

Closes: elastic/security-team#8989

## Description

The Add integration prompt has a number of images that are decorative,
but have alt text added. This could be confusing to screen reader users
because the images do not provide additional context or information.
Let's update them to have `alt=""` attributes so the images are removed
from the accessibility tree. Screenshot attached below.

### Steps to recreate

1. Create a new Security Serverless project if none exist
2. When the project is ready, open it and go to Integrations, under the
Project Settings in the lower left navigation
3. Search for DynamoDB in the Integrations, and click on the card
4. From the DynamoDB detail view, click "Add Amazon DynamoDB"
5. When the "Ready to add your first integration?" view loads, open Dev
Tools and verify the images highlighted have alt text.

### What was done? 
1. _role="presentation"_ was set to image container
2. removed extra `alt`'s attributes

x-pack/plugins/fleet/public/applications/fleet/sections/agent_policy/create_package_policy_page/multi_page_layout/components/add_first_integration_splash.tsx

@@ -60,7 +60,7 @@ const CenteredEuiStepNumber = styled(EuiStepNumber)`
 // step numbers are not centered in smaller layouts without this
 const CenteredEuiImage = (props: EuiImageProps) => (
   <div style={{ margin: '0 auto' }}>
-    <EuiImage {...props} />
+    <EuiImage role="presentation" {...props} />
   </div>
 );
 
@@ -93,10 +93,7 @@ const AddIntegrationStepsIllustrations = () => {
           </EuiFlexItem>
           <EuiFlexItem>
             <div style={{ margin: '0 auto' }}>
-              <CenteredEuiImage
-                alt="Illustration of installing the Elastic Agent"
-                src={assetsBasePath + '1_install_agent.svg'}
-              />
+              <CenteredEuiImage alt="" src={assetsBasePath + '1_install_agent.svg'} />
             </div>
           </EuiFlexItem>
           <EuiFlexItem>
@@ -124,10 +121,7 @@ const AddIntegrationStepsIllustrations = () => {
       </EuiShowFor>
       <EuiHideFor sizes={['s', 'xs']}>
         <EuiFlexItem grow={false}>
-          <CenteredEuiImage
-            alt="Illustration of an arrow pointing from left to right"
-            src={assetsBasePath + 'arrow_right_curve_over.svg'}
-          />
+          <CenteredEuiImage alt="" src={assetsBasePath + 'arrow_right_curve_over.svg'} />
         </EuiFlexItem>
       </EuiHideFor>
       <EuiFlexItem grow={false}>
@@ -136,10 +130,7 @@ const AddIntegrationStepsIllustrations = () => {
             <CenteredEuiStepNumber status="incomplete" number={2} />
           </EuiFlexItem>
           <EuiFlexItem>
-            <CenteredEuiImage
-              alt="Illustration of adding an integration"
-              src={assetsBasePath + '2_add_integration.svg'}
-            />
+            <CenteredEuiImage alt="" src={assetsBasePath + '2_add_integration.svg'} />
           </EuiFlexItem>
           <EuiFlexItem>
             <EuiText textAlign="center">
@@ -166,10 +157,7 @@ const AddIntegrationStepsIllustrations = () => {
       </EuiShowFor>
       <EuiHideFor sizes={['s', 'xs']}>
         <EuiFlexItem grow={false}>
-          <CenteredEuiImage
-            alt="Illustration of an arrow pointing from left to right"
-            src={assetsBasePath + 'arrow_right_curve_under.svg'}
-          />
+          <CenteredEuiImage alt="" src={assetsBasePath + 'arrow_right_curve_under.svg'} />
         </EuiFlexItem>
       </EuiHideFor>
       <EuiFlexItem grow={false}>
@@ -178,10 +166,7 @@ const AddIntegrationStepsIllustrations = () => {
             <CenteredEuiStepNumber status="incomplete" number={3} />
           </EuiFlexItem>
           <EuiFlexItem>
-            <CenteredEuiImage
-              alt="Illustration of a dashboard with data"
-              src={assetsBasePath + '3_confirm_data.svg'}
-            />
+            <CenteredEuiImage alt="" src={assetsBasePath + '3_confirm_data.svg'} />
           </EuiFlexItem>
           <EuiFlexItem>
             <EuiText textAlign="center">