Fix: Exec race condition

[Meldiron]

If you create execution right after build, it tries to create container but that (for some reason) still exist from build. You get error

An internal curl error has occurred while starting runtime! Error Msg: Docker Error: docker: Error response from daemon: Conflict. The container name "/exc0-6504acaa254213470be0-6507566cd981c5675a7f" is already in use by container "3db20471263767d391a7a0d2929eca60be43349b700c84467ca4efeec2c4de34". You have to remove (or rename) that container to be able to reuse that name.
See 'docker run --help'.
Preparing for build ...
Building ...

added 13 packages, and audited 14 packages in 1s

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found 0 vulnerabilities
Packing build ...
Build finished.
\nError Code: 500

To prevent this, we give exec container different name than build container with the suffix. That should fully separate those concerns, and not cause this troble.

[Meldiron]

Closing in favour of appwrite/appwrite#6270