Use exact major version in dockerfiles

[joanhey]

A bench need to be reproducible.
If the dockerfile from don't have an exact major.minor version is impossible.
Ideally major.minor without the patch version is OK.

But never: latest, stable, no version (it's the same than latest), nightly, ....

Examples:

• https://github.com/MDA2AV/HttpArena/blob/main/frameworks/nginx-openresty/Dockerfile#L1
• https://github.com/MDA2AV/HttpArena/blob/main/frameworks/fletch/Dockerfile#L2
• https://github.com/MDA2AV/HttpArena/blob/main/frameworks/carno/Dockerfile#L1
• https://github.com/MDA2AV/HttpArena/blob/main/frameworks/bun/Dockerfile#L1
• https://github.com/MDA2AV/HttpArena/blob/main/frameworks/bun-websocket/Dockerfile#L1
• https://github.com/MDA2AV/HttpArena/blob/main/frameworks/actix-websocket/Dockerfile#L1
• ...

Thank you !!!

[joanhey]

Benny need to learn to do a bench !!