Fix web3 instance after switching chain

[dasanra]

What it solves

Fixes the issue reported in this comment:
#2720 (comment)
It wasn't only related to the create safe step, but in many places we were using a readOnly instance of web3. Most of the cases didn't had issues because it was not used to do queries to the blockchain but just for the unit conversion or parsing. But in those cases where we launch a query to the blockchain it was still initialized with the default chain RPC, so wrong RPC query was send in other chains

How this PR fixes it

We create a new instance of web3ReadOnly for each network, but we cache them as singleton instance in order to avoid creating many new objects

How to test it

Try to create a safe in a chain different than the default one and check that is correctly detected. Also RPC calls can be check in network console, validating that they are done to the correct chain RPC

[github-actions]

CLA Assistant Lite All Contributors have signed the CLA.

[github-actions]

ESLint Summary View Full Report

Annotations are provided inline on the Files Changed tab. You can also see all annotations that were generated on the annotations page.

Type	Occurrences	Fixable
Errors	0	0
Warnings	0	0
Ignored	6	N/A

• Result: ✅ success
• Annotations: 0 total

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^{Report generated by eslint-plus-action}

[github-actions]

• Safe Multisig app polygon

[github-actions]

• Safe Multisig app rinkeby

[github-actions]

• Safe Multisig app mainnet

[github-actions]

E2E Tests Failed
Check the results here: https://github.com/gnosis/safe-react-e2e-tests/actions/runs/1281986143

Failed tests:

• ❌ Add an existing safe Add an existing safe

[DaniSomoza]

Approved!