Adds env var support for setting cache size #248

Job	Run time
apply-label-to-new-pr	3s
check-labels	6s
pull-docker-image	18s
run-unit-test	48s
find-e2e-tests	11s
e2e tests: /home/runner/work/async-substrate-interface/async-substrate-interface/btcli/tests/e2e_tests/test_wallet_creations.py	1m 41s
e2e tests: /home/runner/work/async-substrate-interface/async-substrate-interface/btcli/tests/e2e_tests/test_staking_sudo.py	3m 48s
e2e tests: /home/runner/work/async-substrate-interface/async-substrate-interface/btcli/tests/e2e_tests/test_children_hotkeys.py	2m 10s
e2e tests: /home/runner/work/async-substrate-interface/async-substrate-interface/btcli/tests/e2e_tests/test_hyperparams_setting.py	4m 33s
e2e tests: /home/runner/work/async-substrate-interface/async-substrate-interface/btcli/tests/e2e_tests/test_liquidity.py	3m 36s
e2e tests: /home/runner/work/async-substrate-interface/async-substrate-interface/btcli/tests/e2e_tests/test_senate.py	3m 36s
e2e tests: /home/runner/work/async-substrate-interface/async-substrate-interface/btcli/tests/e2e_tests/test_unstaking.py	3m 40s
e2e tests: /home/runner/work/async-substrate-interface/async-substrate-interface/btcli/tests/e2e_tests/test_root.py	1m 30s
e2e tests: /home/runner/work/async-substrate-interface/async-substrate-interface/btcli/tests/e2e_tests/test_wallet_interactions.py	3m 8s
	29m 8s

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