Reapply "libprocessgroup: Look for memcg v2 MaxActivationDepth override"

This reverts commit c53f9f8d.

webview_zygote is its own user and was attempting to read the metadata
override file, but the /metadata/libprocessgroup directory and the
memcg_v2_max_activation_depth contained therein had directory/file
permissions which were too restrictive and did not allow any readers
other than system. These are now globally readable which matches the
sepolicy for these items.

Bug: 390228674
Ignore-AOSP-First: Reapply reverted commit
Change-Id: I36117b564575b1c2c6538214c025fe5f607866ec