Let `flux` manager update tags and digests (`flux` currently ignores tags)

[HonkingGoose]

Describe the proposed change(s).

Renovate's flux manager does not support updating tags and digests yet:

https://github.com/renovatebot/renovate/blob/8975c9bda67880fd4c91bdc32534e24f98a90e0e/lib/modules/manager/flux/extract.ts#L214

@viceice says Renovate should support updating tags and digests. @viceice will look next week if there's an easy way to add support.

Related Discussion:

• #29521