Rename ambiguous env vars: WS_ENDPOINT, NODE_*_PATTERN

[PierreBesson]

For historical reasons, some environment variables are badly named which makes adoption of the testnet-manager by other teams tedious, eg WS_ENDPOINT should be RELAY_CHAIN_RPC_URL.

Since paritytech/substrate#12663 we have both WS and HTTP on the same server so we should merge the configuration for the WS (NODE_WS_PATTERN) and HTTP (NODE_HTTP_PATTERN) pattern into a single: RPC_NODE_URL_PATTERN.

We should also use POD_NAME instead of NODE_NAME as it is more descriptive.

Other possible changes:

• VALIDATORS_ROOT_SEED -> DERIVATION_ROOT_SEED to make it clear it is used as derivation for both validators and collators.
• TESTNET_MANAGER_CONSENSUS -> RELAY_CHAIN_CONSENSUS
• NETWORK_SS58_FORMAT -> RELAY_CHAIN_SS58_FORMAT (parachain can have a different ss58 format)

Question: should we prefix all env vars by MANAGER_ ?

[lazam]

#93