feat: allow custom truncation suffix

[pauldambra]

when adding https://github.com/rrweb-io/rrweb/pull/1530 I realised that there's code in the console plugin for truncation that we're copying so our users have to download twice (not much but every little helps)

the only difference is we use (and some code expects) a different truncation marker

so, this

• lets you add a custom truncation marker
• and actively truncates strings not just objects that are being toString-ed