[FEAT] Implement pool management modals

[yurixander]

Currently, creating & joining pools is already possible. However, once someone creates a pool, they may need to manage certain properties around it: adjusting the commission rate, updating nominations, etc.

• When the active user has the corresponding role (ex. root, nominator, bouncer), show the appropriate action button (ex. Update Roles, Update Nominations, etc.).
• When the action button is clicked, its corresponding modal should be shown.
• For the root role, a modal containing inputs with the different roles, and also the commission rate
• For the nominator role, a 'Select validators' modal similar to the one used in the Nominations page
• For the bouncer role, a dropdown to choose the pool state (whether closed or open)