Add option to change "Insert into Post" text button for specific upload form

[alexvorn2]

A lot of developers have a custom admin panel for uploading images and other media files, but having the text "Insert into Post" in the button does not seems to be correct.

It will be great to introduce a specific hook function for such thing, or to make the text to be "Insert into form" - for other pages that are not into the edit.php.

[ocean90]

#21092, #21390