Add possibility to set and combine multiple profiles

[lukfor]

This PR fixes #94.

Basic Profile Usage

By default, nf-test reads the profile configuration from nf-test.config. If you've defined a profile called A in nf-test.config, running nf-test --profile B will start Nextflow with only the B profile. It replaces any existing profiles.

Combining Profiles with "+"

To combine profiles, you can use the + prefix. For example, running nf-test --profile +B will start Nextflow with both A and B profiles, resulting in -profile A,B. This allows you to extend the existing configuration with additional profiles.

Profile Priority Order

Profiles are evaluated in a specific order, ensuring predictable behavior:

1. Profile in nf-test.config: The first profile considered is the one defined in nf-test.config.

2. Profile Defined in Testcase: If you specify a profile within a testcase, it takes precedence over the one in nf-test.config.

3. Profile Defined on the Command Line (CLI): Finally, any profiles provided directly through the CLI have the highest priority and override/extends previously defined profiles.

By understanding this profile evaluation order, you can effectively configure Nextflow executions for your test cases in a flexible and organized manner.