Custom Network: Block Explorer URL must be a valid `http[s]:` protocol URL

[wachunei]

As user, I want to optionally add a block explorer URL when adding a custom network. In case the URL is not a http:///https: I want to be warned and prevented from adding an invalid URL

As developer, I want to make sure blockExplorerURL is a valid URL.

[ibrahimtaveras00]

if adding block explorer with www it will show that in the burger menu

if not adding https:// it will show up as undefined

The sweet spot is when www is removed, so you'd have https://bscscan.com/

[omnat]

Add validation on the custom network adding form:

1. Enforce an HTTPS:// (not HTTP)
2. Validation that this is a valid URL