Add MultiSource Parameter Type

[smt5541]

🛠 Changes being made

Give examples of the changes you've made in this pull request. Include an itemized list if you can.

• Add Parameter subclass MultiSource
• Update ValidateParameters#validate to handle expected_delivery_types as a list of Parameters, return the first successful match, or error if no match found in any of the types

🧠 Rationale behind the change

Why did you choose to make these changes?

• It would be useful in certain cases to be able to accept parameters from multiple sources, possibly spanning multiple HTTP methods.

Does this pull request resolve any open issues?

Yes. Closes #43

Were there any trade-offs you had to consider?

Usage syntax and behavior customization:

string: str = MultiSource(Query, Json, min_int=0) - can't specify validation conditions per parameter type, but it's easier to write out
string: str = MultiSource([Query(min_int=0), Json(min_int=0) - could allow for more customization in usage, but for the average user it's a worse experience

🧪 Testing

• Have tests been added or updated for the changes introduced in this pull request?

• Are the changes backwards compatible?

If the changes aren't backwards compatible, what other options were explored?

✨ Quality check

• Are your changes free of any erroneous print statements, debuggers or other leftover code?

• Has the README been updated to reflect the changes introduced (if applicable)?

💬 Additional comments

Feel free to add any further information below

Dependent on #45

[Ge0rg3]

Great addition, many thanks