Make dora versions compatible by using separate versioning for `dora-message` crate

[phil-opp]

By versioning the dora-message crate individually, we can use the semver rules to encode which versions are compatible. This way, we can allow different versions of dora to work together (e.g. CLI version can be different than node API version), as long as the message formats are compatible. Breaking message format changes are signaled by a semver-incompatible release of dora-message. For example, 0.4.0 is not compatible with 0.3.5.

One alternative approach could be to use the main version to signal compatibility, i.e. the common version that we use for all dora crates. This has the disadvantage that we might need to bump the minor version of the main dora crate every time we want to change the message format in a breaking way. As we still expect semi-regular breaking changes to the message format in the near future, we want to avoid this churn. Once we consider the message format more stable, we plan to revisit this approach.

Fixes https://github.com/dora-rs/dora/issues/504

TODO

• [x] Update release script: We should not try to publish the dora-message crate if there is no new version.
• [x] Relax version checks to only compare major/minor version (according to semver compatibility rules).