feat: expose exclusion pattern for async-inject-variables as configuration var

[vidbina]

Some variables matching the pattern org-babel-* caused some trouble because they had propertized texts for values and thus weren't serializable in a manner that didn't break reading attempts.

Since async-inject-variables allows for the definition of exclusion patterns, I simply used this to reduce the set of vars that actually get injected into the async process.

The default value for the exclusion pattern will drop variables that contain -overlay as part of their names since these typically contain overlays which have those propertized texts in my setup.

The previous variable ob-async-inject-variables has been kept as an alias for backwards compatibility.

[vidbina]

I have some notes in my literate config on what the issue was if more details are helpful https://github.com/vidbina/dotfiles/tree/reorg-for-lit-prog/emacs#debug-invalid-read-read-syntax-error-during-variable-injection