Release of Vitess v15.0.3

The entire changelog for this release can be found here.

The release includes 52 commits (excluding merges)

Thanks to all our contributors: @GuptaManan100, @ajm188, @dbussink, @deepthi, @frouioui, @harshit-gangal, @mattlord, @rsajwani, @shlomi-noach, @systay, @vitess-bot[bot], @vmg