feat(framework): make assets path configurable

[vladitasev]

This has been a highly requested feature for a long time. Although resource path is a build-time artefact, it often makes sense to build once and deploy in multiple, previously unknown directories.

Changes:

• New configuration setting: assetsPath
• Users have the capability to build with DEPLOY_PUBLIC_PATH or to use assetsPath at runtime (or both).

Option1: build-time

DEPLOY_PUBLIC_PATH=/my/resources/ yarn build

(for Windows: DEPLOY_PUBLIC_PATH="\/my\/resources\/" yarn build)

Option2: runtime

	<script data-ui5-config type="application/json">
		{
			"assetsPath": "/my/resources/"
		}
	</script>

BREAKING CHANGE: Running the production build command: yarn build will now generate the .json resources asset paths without /resources/ in the beginning. The yarn start command remains unchanged - it will implicitly set DEPLOY_PUBLIC_PATH to /resources/ as before.

Before the change, the build generates for example:

var SAPIcons = "/resources/SAP-icons.33a03c68298d0449.json";
registerIconBundle("SAP-icons", SAPIcons);

After the change, without setting DEPLOY_PUBLIC_PATH it will generate:

var SAPIcons = "SAP-icons.33a03c68298d0449.json";
registerIconBundle("SAP-icons", SAPIcons);

In order to have the old yarn build behavior run:

DEPLOY_PUBLIC_PATH=/resources/ yarn build

(for Windows: DEPLOY_PUBLIC_PATH="\/resources\/" yarn build)

closes: #2167
closes: #2169
related to: #2205

[ilhan007]

I think this would also resolves the 2nd part of this issue #2169
"2. It does not have a clean solution to identify a dynamic subdirectory where all the translations for a library should come from"

[pskelin]

two minor documentation fixes, otherwise looks good

[pskelin]

this is DEPLOY_PUBLIC_PATH

[pskelin]

It might be good to add the example from the commit description in the docs
DEPLOY_PUBLIC_PATH="\/my\/resources\/" yarn build

note however that this gives the wrong result on mac (when reading from nodejs)
DEPLOY_PUBLIC_PATH: '\\/my\\/resources\\/'