consensus: Create a distinctive signature for the agreement

[goshawk-3]

Describe the bug
As reported by @fed-franz, consensus computes same signatures for signing both agreement and 2nd reduction messages.

To create a distinctive signature we may consider signing topic id together with ( Round | Step | BlockHash ).

Expected behaviour
Any signature must be distinctive .

Logs/Screenshot

2nd Reduction

main{round=4 step=3 name="2nd_red" pk="rm6jwcM9xQChnVeH"}: dusk_consensus::aggregator: event="vote aggregated" hash="af75f916ab3e2455...d4d4f5cdba79462f" from="uazLgN2HtLqaDZCx" added=17 total=17 target=43 signature="b8b686753fd464ba...3485b4ca421ff325"
main{round=4 step=3 name="2nd_red" pk="rm6jwcM9xQChnVeH"}: dusk_consensus::aggregator: event="vote aggregated" hash="af75f916ab3e2455...d4d4f5cdba79462f" from="rm6jwcM9xQChnVeH" added=21 total=38 target=43 signature="87f4272b9931a498...215ce5e313c757d9"
main{round=4 step=3 name="2nd_red" pk="rm6jwcM9xQChnVeH"}: dusk_consensus::aggregator: event="vote aggregated" hash="af75f916ab3e2455...d4d4f5cdba79462f" from="23RRcwBV2BsBVvmN" added=10 total=48 target=43 signature="83c0989630d97591...77f53f627cf90bfa"


Agreements

agr_task{round=4 pubkey="rm6jwcM9xQChnVeH"}:acc_task: dusk_consensus::agreement::accumulator: event="agreement accumulated" hash="af75f916ab3e2455...d4d4f5cdba79462f" from="rm6jwcM9xQChnVeH" added=21 total=21 signature="87f4272b9931a498...215ce5e313c757d9"
agr_task{round=4 pubkey="rm6jwcM9xQChnVeH"}:acc_task: dusk_consensus::agreement::accumulator: event="agreement accumulated" hash="af75f916ab3e2455...d4d4f5cdba79462f" from="uazLgN2HtLqaDZCx" added=17 total=38 signature="b8b686753fd464ba...3485b4ca421ff325"
agr_task{round=4 pubkey="rm6jwcM9xQChnVeH"}:acc_task: dusk_consensus::agreement::accumulator: event="agreement accumulated" hash="af75f916ab3e2455...d4d4f5cdba79462f" from="23RRcwBV2BsBVvmN" added=10 total=48 signature="83c0989630d97591...77f53f627cf90bfa"
agr_task{round=4 pubkey="rm6jwcM9xQChnVeH"}:acc_task: dusk_consensus::agreement::accumulator: event="agreement accumulated" hash="af75f916ab3e2455...d4d4f5cdba79462f" from="xxRf7HtmFrcNqF8Q" added=16 total=64 signature="b289682eb5227dc6...71419e80e926f8ee"

[herr-seppia]

Resolved in #1264