[Feature] Make Summary, Feature and Evidence tables optional

[nilshoffmann]

Is your feature request related to a problem? Please describe.
For certain use cases (e.g. XCMS), not all tables are populatable immediately.
However, the existing tables and file should still be validatable. At the moment, the spec does not allow omission of the SML, SMF or SME tables.

Describe the solution you'd like
We would like to update the specification, such that

1. MTD is always mandatory
2. SML is not mandatory, if at least MTD + SMF exist, or MTD + SMF + SME
3. SMF is not mandatory, if at least MTD + SML exist, SME cannot exist without SMF
4. SME is not mandatory, it at least MTD + SMF exist, (or MTD + SML + SMF -> questionable if this makes sense)

Describe alternatives you've considered
Alternatively, the tables could be left in the file as empty tables, e.g. just with the header row and no content rows. However, this would not add any semantic context.

Submitter Tasks

• Provide a pull request (Please add the link)
• Schema: Update mzTab_m_openapi.yml (View File)
• Specification: Update mzTab_format_specification_2_1-M.adoc with an example (View File)
• Example files: if possible, modify an existing or add a new example file (Existing example files)

Maintainer & WG Tasks

• Triage: Assign labels and Milestones to this issue.
• Discuss and review and approve PR.

Next Steps, once we reach an agreement on the changes above:

• Create a downstream issue in the jmzTab-m repo (https://github.com/lifs-tools/jmzTab-m/issues)
• Implement and test changes in jmzTab-M
• Implement changes in R & Python implementations

[nilshoffmann]