nomination-pools: Make max points to balance ratio configurable

[emostov]

When a delegator attempts to join a nomination pool we ensure that the current points to balance ratio of the pool is less than 10. Instead of 10 this should be a pallet config option.

Should wait until #10694 is merged to start working on this.

Originally posted by @kianenigma in #10694 (comment)

[Doordashcon]

Hello @emostov I want to attempt this issue

[emostov]

Hi @Doordashcon - thank you for the interest in contributing. Unfortunately I initially miss-wrote this issue because I failed to mention that work for a PR addressing this issue should only start after #10694 is merged. Feel free to follow up after that.

[kianenigma]

@emostov provide a bit more context here, if any? I think this will be a good candidate for @rossbulat to tackle.

[rossbulat]

Thank you @kianenigma , awaiting #10694 before implementing.

For reference, logic to be amended once the config item is introduced:

lib.rs: ensure at 598.

tests.rs: asserts at 197, 201 and 490.