Attachment point enumeration logic works wrong

[AlexeyGirin]

Steps to Reproduce

1. Load from file: Attachment point enumeration logic works wrong.zip
   OR manually create following configuration on the canvas:
   
2. Add attachment point (via context menu) to any atom
   

Actual behavior
System adds R9 labeled attachment point

Expected behavior
System adds R2 labeled attachment point

As per requirements:

Erase logic (since system enumerate AP automatically). What if we have R1, R2, R3 and I delete R2 and add NEW AP? What if we
have R1-R8 in place and I delete R2 and try to add new AP?
Gaps should start be filled if we rich the R8 (later this will be changed to let user choose AP name himself)

Versions:

• Indigo Toolkit Version 1.21.0-rc.1.0-g9194599b2-wasm32-wasm-clang-19.0.0
• Ketcher Version 2.22.0-rc.2 Build at 2024-06-03; 18:43:00
• Chrome Version 125.0.6422.142 (Official Build) (64-bit)
• Windows 10

Issue found while testing #4530

[AnnaKosol]

Verified

2024-07-02.15.57.52.mov

Versions:
Ketcher Version 2.23.0-rc.1 Build at 2024-07-02; 09:03:38
Indigo Version 1.21.0-rc.1.0-g9194599b2-x86_64-linux-gnu-11.2.1
MacOs Sonoma version 14.5
Chrome Version 126.0.6478.127 (Официальная сборка), (arm64)