Added block timestamp + scripts update for the round duration

[iulianpascalau]

Reasoning behind the pull request

• added block timestamp + scripts update for the round duration
• added the possibility to define the round duration in the local scripts (related PR: added round duration mx-chain-deploy-go#52)

Proposed changes

Testing procedure

• standard system test
• test that the proxy's API endpoint route /network/status/0, /network/status/1 ... /network/status/4294967295 returns the new field called erd_block_timestamp that matches the block's timestamp.

Pre-requisites

Based on the Contributing Guidelines the PR author and the reviewers must check the following requirements are met:

• was the PR targeted to the correct branch?
• if this is a larger feature that probably needs more than one PR, is there a feat branch created?
• if this is a feat branch merging, do all satellite projects have a proper tag inside go.mod?

[gabi-vuls]

Normal allin test: v1.6.15-dev-config-eb2e06c06d -> add-block-timestamp-in-net-bd41b675cd

--- Specific errors ---

block hash does not match 213
wrong nonce in block 175
miniblocks does not match 0
num miniblocks does not match 0
miniblock hash does not match 0
block bodies does not match 1
receipts hash missmatch 0

/------/

--- Statistics ---

Nr. of all ERRORS: 0
Nr. of all WARNS: 227
Nr. of new ERRORS: 0
Nr. of new WARNS: 0
Nr. of PANICS: 0

/------/

--- ERRORS ---

/------/

--- WARNINGS ---

/------/