Manifests from main does not work due to read only filesystem.

[bwplotka]

This is fine on managed GMP, because we have a different flow there.

Using manifests/* from main leads to:

{"error":"create temporary certificate dir: mkdir /tmp/operator-cert2628617008: read-only file system"

[bwplotka]

Introduced by https://github.com/GoogleCloudPlatform/prometheus-engine/pull/944, but not a biggie.

~Probably the best to be fixed by something like https://github.com/GoogleCloudPlatform/prometheus-engine/pull/663~, actually fixed on main already (build latest main operator, but can't really figure out how it was fixed), just manifests can't reference the latest main image.

TODO: Figure out the best way forward, some relevant discussion here: https://github.com/GoogleCloudPlatform/prometheus-engine/pull/1010#discussion_r1634274765

[bwplotka]

Ok, actually we have chicken and egg problem with main until releases happen or no breaking changes are there. Even with https://github.com/GoogleCloudPlatform/prometheus-engine/pull/1147 which fixes readonly problem we now merged reduced permissions. Users should use release branches instead, let's update docs instead.