feat: Cache workspace blob on tofu-controller filesystem

[yitsushi]

• block stream encryption + remove non-stream endpoint
• Nothing uses the feature yet.

❯ kubectl exec -it -n flux-system chart-tofu-controller-648fbc54f8-7sprc -- ls -la /blob-cache/
total 12
drwxrwsrwx    2 root     1337          4096 Dec 19 15:29 .
drwxr-xr-x    1 root     root          4096 Dec 19 15:29 ..
-rw-r--r--    1 controll 1337           800 Dec 20 09:41 terraform-helloworld-tf-priv.tar.gz

❯ kubectl exec -it -n flux-system chart-tofu-controller-648fbc54f8-7sprc -- hexdump -C /blob-cache/terraform-helloworld-tf-priv.tar.gz | head -n 3
00000000  1b 3f 00 8d 25 67 17 79  87 04 d7 b9 03 f2 6c ba  |.?..%g.y......l.|
00000010  bc 0c 7e 75 29 de 25 1f  bb 99 c4 49 2d 99 1b e0  |..~u).%....I-...|
00000020  b3 72 2f ca ab fb 5f 93  ee b4 ba bd a6 76 83 38  |.r/..._......v.8|

with a small go temp app, after decryption and untar (the repo itself has only one file: main.tf):

❯ kubectl cp -n flux-system chart-tofu-controller-648fbc54f8-7sprc:/blob-cache/terraform-helloworld-tf-priv.tar.gz ./terraform-helloworld-tf-priv.tar.gz
tar: removing leading '/' from member names

❯ go run .
INFO[0000] /tmp/1417200660

❯ tree /tmp/1417200660
/tmp/1417200660
├── backend_override.tf
├── generated.auto.tfvars.json
└── main.tf

1 directory, 3 files

Extra To Do items:

• Add feature flag