Staking: Copy update for restake

[josietyleung]

Existing: Restaking's flow looks the same as staking which can be confusing for users as they don't know they are switching or staking from the beginning.

Steps to reproduce:

1. At individual asset page
2. Select 'switch validator'
3. Lands at select validator page

Expected: When user is restaking, the select validator page should read 'Select a new validator', instead of 'Select a validator'

[clockworkgr]

@caudurodev Sorry, I picked this up in the process of implementing a couple of other fixes...