docs - some terminology changes for inclusivity

[lisakowen]

update some of the terms to be more inclusive, including disable, execute, kill.

add alt-text to the diagrams; this required that i change to markdown image format.

doc review site link, if interested (behind vpn): https://docs-staging.vmware.com/en/VMware-Tanzu-Greenplum-Platform-Extension-Framework/lisa-review2/tanzu-greenplum-platform-extension-framework/GUID-overview_pxf.html