[FW][FIX] ColorPicker: modified add custom color icon

[fw-bot]

Description:

Fixed the positioning of the add custom color icon, replacing the hardcoded version with an SVG icon for improved visual appeal.

Odoo task ID : 3258627

review checklist

• feature is organized in plugin, or UI components
• support of duplicate sheet (deep copy)
• in model/core: ranges are Range object, and can be adapted (adaptRanges)
• in model/UI: ranges are strings (to show the user)
• undo-able commands (uses this.history.update)
• multiuser-able commands (has inverse commands and transformations where needed)
• new/updated/removed commands are documented
• exportable in excel
• translations (_lt("qmsdf %s", abc))
• unit tested
• clean commented code
• track breaking changes
• doc is rebuild (npm run doc)
• status is correct in Odoo

Forward-Port-Of: #2493
Forward-Port-Of: #2324

[robodoo]

Pull request status dashboard.

[fw-bot]

@aath-odoo @rrahir this PR targets master and is the last of the forward-port chain.

To merge the full chain, say

@fw-bot r+

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port

[rrahir]

@fw-bot r+