Enrich current analyses and introduce new ones

[RiboRings]

Some missing analyses could be added, for example:

• differential abundance
• association (mediation and correlation)
• networks

[RiboRings]

Related to this issue, enrich the current options for alpha and beta diversity. In particular, we can easily add support for:

• more alpha metrics (check if there is a way to provide all metrics from mia without hard-coding them)
• more dimensionality reduction methods, like UMAP and TSNE (any other relevant ones?
• more beta diversity indices (also here, check if there is a way to fetch all options from vegan::vegdist)

[RiboRings]

Clustering analysis was introduced in #27