Added pauseCallback in amp-ima-video

[micajuine-ho]

Closes #23365

Need to have pauseCallback() implemented, so that we can pause resources (amp-ima-video) when they are not visible anymore

amphtml/src/service/resource.js

Lines 981 to 986 in ec0adfc

	pause() {
	this.element.pauseCallback();
	if (this.element.unlayoutOnPause()) {
	this.unlayout();
	}
	}

[calebcordry]

Thanks for digging into this! Might want to wait for @alanorozco expert approval :)