Update documentation - Adobe Commerce authentication keys

[hardyjohnson]

• Updates documentation to point to the current Adobe Commerce URL explaining the process for generating or locating Composer authentication keys for Adobe Commerce Marketplace and third party packages.

[hardyjohnson]

Note @navarr just going through the docs, will see if I can update the rest of the old Magento2 devdocs links, LMK if it is preferable to fixing them in one PR. I think there are 4-6 throughout somewhere.

[navarr]

@hardyjohnson I appreciate the contribution!

Feel free to do them all at once or piecemeal, I can process them either way!