Update the block production workflow to use the block V3 API by default

[mehdi-aouadi]

Description

Currently the block production have two APIs: block v2 and block v3. In the current block V3 flow, the blinded param (similar to the block V2 API) is hard coded and set to true. The following changes are required to make the block V3 API the default:

• Make the block production automatically choose blinded or unblinded blocks #7889
  • Allow block creation to defer blinded/unblinded decision #7835
  • Remove the hard coded blinded param in block V3
• Enabled block V3 as the default
• Test compatibility among CLs
• For next release:
• Remove the deprecated block V2 methods - done via (Remove deprecated GetNewBlindedBlock #8508 and Remove deprecated GetNewBlockV2 from Validator API #8504)
• Remove the --Xblock-v3-enabled option which is used to use block V3 apis (Remove --xblock-v3-enabled and useBlindedBlock variable #8511)

These are the last steps of #7390

[gfukushima]

Closing this as last PR was merged today.