Add bold-trnL for plant taxonomic classification with DADA2

[Sofokli5]

Closes #843

This is the first PR of more to follow that aim to add plant databases to the pipeline. Starting with bold database and trnL marker.
Tested locally and worked fine.

PR checklist

• This comment contains a description of changes (with reason).
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added a new tool - have you followed the pipeline conventions in the contribution docs
• If necessary, also make a PR on the nf-core/ampliseq branch on the nf-core/test-datasets repository.
• Make sure your code lints (nf-core pipelines lint).
• Ensure the test suite passes (nextflow run . -profile test,docker --outdir <OUTDIR>).
• Check for unexpected warnings in debug mode (nextflow run . -profile debug,test,docker --outdir <OUTDIR>).
• Usage Documentation in docs/usage.md is updated.
• Output Documentation in docs/output.md is updated.
• CHANGELOG.md is updated.
• README.md is updated (including new tool citations and authors/contributors).

[nf-core-bot]

Warning

Newer version of the nf-core template is available.

Your pipeline is using an old version of the nf-core template: 3.2.0.
Please update your pipeline to the latest version.

For more documentation on how to update your pipeline, please see the nf-core documentation and Synchronisation documentation.

[d4straub]

Looks good, but versioning is required.

[d4straub]

Great, looks good to me!
Please make sure that you work in future on the dev branch, the branch that was used here looks like the master branch.

Edit: You can merge the PR now!