[🚀esl-image]: simplify `lazy` handling

[ala-n]

As an ESL architect/user, I want consistent handling for lazy loading across components.

In bounds of #1641, a different approach for handling lazy processes was introduced:

• no lazy attribute = no block for loading
• lazy attribute -> blocking load process, IO observation success leads to removal of lazy attribute

Current esl-image behavior based on the separate lazy-triggered attribute

Request to change esl-image lazy processing to the following flow:

• no lazy attribute = no loading block
• lazy='manual' = blocks image loading until the lazy attribute is removed (manually by DOM mutation or by the call of triggerLoad() method)
• lazy='auto' (or lazy w/o value) = blocks image loading until the lazy attribute is automatically removed by IO