WIP: Compress extensions for S3

[bayandin]

Problem

We want to upload compressed extensions + have an index file for them.

Summary of changes

• Move the list of buckets to GitHub repo variables.
• Pack several extensions as an example into tar.zstd file (zstd is smaller and faster than gz: https://gist.github.com/bayandin/43b4d9419be8ce4398663c26730b22a0)
• TODO: add index file for them Create ext_index.json #4764

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

1040 tests run: 988 passed, 0 failed, 52 skipped (full report)

---

Flaky tests (2)

Postgres 15

• test_remote_storage_upload_queue_retries[local_fs]: debug
• test_remote_timeline_client_calls_started_metric[local_fs]: release

[awestover]

Note: there is a slight discrepancy between the layout of files created here and the assumed layout in rust code.

Rust assumes a layout like this:

5615610098 // this is an extension build number
├── v14
│   ├── extensions
│   │   ├── anon.tar.zst
│   │   └── embedding.tar.zst
│   └── ext_index.json
└── v15
    ├── extensions
    │   ├── anon.tar.zst
    │   └── embedding.tar.zst
    └── ext_index.json
5615261079
├── v14
│   ├── extensions
│   │   └── anon.tar.zst
│   └── ext_index.json
└── v15
    ├── extensions
    │   └── anon.tar.zst
    └── ext_index.json

currently, this PR creates files like this:

5615610098 // this is an extension build number
├── v14
│   ├── extensions
│   │   ├── anon/anon.tar.zst
│   │   └── embedding/embedding.tar.zst
│   └── ext_index.json
└── v15
    ├── extensions
    │   ├── anon/anon.tar.zst
    │   └── embedding/embedding.tar.zst
    └── ext_index.json
5615261079
├── v14
│   ├── extensions
│   │   └── anon/anon.tar.zst
│   └── ext_index.json
└── v15
    ├── extensions
    │   └── anon/anon.tar.zst
    └── ext_index.json

I think the layout assumed in rust is nicer, but not sure if you were planning on having multiple archive files in each of these subdirectories?
It's an easy python or rust fix too if you'd rather keep this layout

[bayandin]

Merged in #4764