docs: add Milvus 2.6 version recognition documentation

[AlintaLu]

This pull request adds documentation to clarify how the Milvus Operator recognizes and manages Milvus component versions, especially in the context of recent changes starting from version 2.6. The update provides guidance on how the operator parses image tags, and what to do when using custom or non-semver images.

Milvus version recognition and configuration:

• Added a new section explaining how the Milvus Operator detects the Milvus version from the spec.components.image tag, and how it handles component changes introduced in Milvus 2.6 (such as the addition of StreamingNode, removal of IndexNode, and merging of coordinators into MixCoord).
• Provided instructions for users of custom or private images on how to explicitly specify the Milvus version using the spec.components.version field when the image tag does not follow semantic versioning.
• Included tips and examples to help users ensure their version strings are semver-compliant, with a link to a semver-check tool.

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AlintaLu

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [AlintaLu]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment