[DOCS] Update screenshot of the "Getting started" page

[nastasha-solomon]

Update the screenshot of the Getting started page to account for these changes:

• [Security Solution] Tweak Text on Getting Started Page kibana#130384 (will be merged in 8.2.1 [8.2] [Security Solution] Tweak Text on Getting Started Page (#131808) kibana#131823 still open, not merged into 8.2 yet)
• https://github.com/elastic/security-team/issues/3530 (merged in 8.3)

[nastasha-solomon]

Assigning to 8.3.0 as per this elastic/kibana#131808

cc: @stephmilovic

[nastasha-solomon]

Adding the 8.2.1 label since elastic/kibana#131808 will be backported to 8.2. Tried grabbing a screenshot of the new page from siem.dev, but the server is still showing the "old" version. Will wait till the next 8.2.1 BC to grab one and open a 7.2.1 PR.

cc: @jmikell821

[nastasha-solomon]

New page design in 8.3: