Change new shell command ids to be random letters

[Taitava]

Quote from me: #151 (comment):

ID should be random instead of sequential

Currently, shell command ids are just sequential numbers starting from 1 0 (corrected on 2022-08-19). I want to change them to alphanumeric random strings, something like 5 characters long (or longer), to avoid the chance to overlap with existing shell command ids when importing. Existing shell commands that now have a numeric id, will keep the same id without changes, as possible hotkeys are dependent on the id.

The minimum length of alphanumeric ids is currently set to 10:

obsidian-shellcommands/src/IDGenerator.ts

Line 25 in 0f1756a

private readonly min_length = 10,

The length can be shortened later if 10 characters is too ugly, but let's keep it as-is for now.

Alphanumeric ids are already used for:

• Custom variables
• Prompts