Update reference hardware and lower CI machine specs

[ghzlatarev]

Description

• Update the reference hardware that we use for generating weights to c6i.4xlarge as per https://wiki.polkadot.network/docs/maintain-guides-how-to-validate-polkadot#standard-hardware
• Reduce all other machine specs to c5.2xlarge to reduce costs (from c5.9xlarge and metal)

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Before we can approve this PR for merge, please make sure that all the following items have been checked off:

• Connected to an issue with discussion and accepted design using zenhub "Connect issue" button below
• Added one label out of the L- group to this PR
• Added one or more labels from the A- and C- groups to this PR
• Explicitly labelled A-calamari and/or A-manta if your changes are meant for/impact either of these (CI depends on it)
• Re-reviewed Files changed in the Github PR explorer.

Situational Notes:

• If adding functionality, write unit tests!
• If importing a new pallet, choose a proper module index for it, and allow it in BaseFilter. Ensure every extrinsic works from front-end. If there's corresponding tool, ensure both work for each other.
• If needed, update our Javascript/Typescript APIs. These APIs are officially used by exchanges or community developers.
• If modifying existing runtime storage items, make sure to implement storage migrations for the runtime and test them with try-runtime. This includes migrations inherited from upstream changes, and you can search the diffs for modifications of #[pallet::storage] items to check for any.

[github-actions]

✅ Congestion test: 1-day congestion cost (manta-runtime) is above the target daily congestion cost

[github-actions]

⚠️ Congestion test: 1-day congestion cost (calamari-runtime) is NOT above the target daily congestion cost

[anaye1997]

LGTM