Allow /local/path for *_URL parameters within config file

## Problem

As a dev I may frequently modify `go-algorand` or `indexer` code on my local file system. I don't want to push to GitHub each change prior to testing the build using `sandbox`. Currently, supplying `/path/to/my/repo` for _ALGOD_URL_ field within **my.config** configuration file results in the error "fatal: /path/to/my/repo does not exist". I'll make the assumption the _INDEXER_URL_ behaves similarly.

## Solution

Proposed by @joe-p:

1. Comment out this line: https://github.com/algorand/sandbox/blob/ef26221e9eb7141482234d061950e8a807f07a0c/images/algod/install.sh#L61
```
git clone --single-branch --branch "${BRANCH}" "${URL}"
```
2. Then add a COPY command similar to this line that copies in the repo to the container: https://github.com/algorand/sandbox/blob/ef26221e9eb7141482234d061950e8a807f07a0c/images/algod/Dockerfile#L29
```
COPY . /tmp
```
3. investigate/modify for `indexer` as well.

4. Solution should parse the _URL_ field value and switch based on the source.

## Dependencies

None known.

## Urgency

Nice to have.

h/t @riolavigne