feat: Allow explorer to be hosted in a subdirectory

[daanporon]

What this PR does / why we need it:

Currently the Hyperledger explorer can only be hosted at the root of a domain name. With this change it's possible to also host it at a subdirectory of a domain for example: https://example.com/your-fabric-explorer-instance.

In order to allow this i added the "homepage" property to the package.json as is described in the create-react-app documentation. By using "." for the homepage you it will always fetch the static files relative too where the explorer is being hosted, this way you don't need to change anything at build time.

Next to that i also changed the location of the api operations to use relative urls as well. This works since a hash-based routing is currently being used.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Additional documentation, usage docs, etc.:

[suumona]

hi @daanporon,
Thanks for the PR. After adding the file changes, the Explorer application isn't reflecting the modifications. To ensure clarity, could you please provide screenshots demonstrating the Explorer being hosted in a subdirectory

[daanporon]

Hi @suumona, this is what i mean. We are using a /insights/some-name url.