### Description

After the release for Airflow 2.6.0 I was integrating some forms into our setup and was missing some options selections - and some nice features to make selections user friendly.

I'd like do contribute some few features into the user forms:
* A select box option where proposals are made but user is not limited to hard `enum` list (`enum` is restricting user input to only the options provided)
* A multi-option pick list (because sometimes a single selection is just not enough
* Labels so that technical values used to control the DAG are different from what is presented as option to user

### Use case/motivation

After the initial release of UI trigger forms, add more features (incrementially)

### Related issues

Relates or potentially has a conflict with #31299, so this should be merged before.

### Are you willing to submit a PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

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"""DAG demonstrating various options for a trigger form generated by DAG params.
The DAG attribute `params` is used to define a default dictionary of parameters which are usually passed
to the DAG and which are used to render a trigger form.
"""
from __future__ import annotations
import datetime
import json
from pathlib import Path
from airflow import DAG
from airflow.decorators import task
from airflow.exceptions import AirflowSkipException
from airflow.models.dagrun import DagRun
from airflow.models.param import Param
from airflow.models.taskinstance import TaskInstance
with DAG(
    dag_id=Path(__file__).stem,
    description=__doc__[0 : __doc__.find(".")],
    doc_md=__doc__,
    schedule=None,
    start_date=datetime.datetime(2022, 3, 4),
    catchup=False,
    tags=["example_ui"],
    params={